Okay here is the skinny:

I'm using Red Hat Enterprise 3.0 which comes with libxml2 1.5.11.  I ran the configure script for php 5.0.3 and it succeeded; however, the build failed.

To resolve the issue I had to upgrade to libxml2 1.6.x ( I chose 1.6.16).  

My complaint is that the configure script should check for 1.6.x version of libxml2?

libxml2 2.5.10 is the minimum version required.
Please paste the errors you got here when compiling.

Redhat Enterprise Linux 3 comes with libxml-2.5.10. But I'm getting compilation errors anyway:

gcc  -Iext/soap/ -I/usr/src/redhat/BUILD/php-5.0.3/ext/soap/ -DPHP_ATOM_INC -I/usr/src/redhat/BUILD/php-5.0.3/include -I/usr/src/redhat/BUILD/php-5.0.3/main -I/usr/src/redhat/BUILD/php-5.0.3 -I/usr/src/redhat/BUILD/php-5.0.3/Zend -I/usr/include/libxml2 -I/usr/include/freetype2 -I/usr/include/imap -I/usr/kerberos/include -I/vrmd/webserver/mhash/include -I/usr/include/mysql -I/usr/include/pspell  -I/usr/src/redhat/BUILD/php-5.0.3/TSRM  -I/usr/kerberos/include  -c /usr/src/redhat/BUILD/php-5.0.3/ext/soap/php_encoding.c -o ext/soap/php_encoding.o  && echo > ext/soap/php_encoding.lo
/usr/src/redhat/BUILD/php-5.0.3/ext/soap/php_encoding.c: In function `to_zval_string':
/usr/src/redhat/BUILD/php-5.0.3/ext/soap/php_encoding.c:498: warning: initialization makes pointer from integer without a cast
/usr/src/redhat/BUILD/php-5.0.3/ext/soap/php_encoding.c: In function `to_zval_stringr':
/usr/src/redhat/BUILD/php-5.0.3/ext/soap/php_encoding.c:534: warning: initialization makes pointer from integer without a cast
/usr/src/redhat/BUILD/php-5.0.3/ext/soap/php_encoding.c: In function `to_zval_stringc':
/usr/src/redhat/BUILD/php-5.0.3/ext/soap/php_encoding.c:570: warning: initialization makes pointer from integer without a cast
/usr/src/redhat/BUILD/php-5.0.3/ext/soap/php_encoding.c: In function `to_xml_string':
/usr/src/redhat/BUILD/php-5.0.3/ext/soap/php_encoding.c:638: warning: initialization makes pointer from integer without a cast

and later:

gcc  -Imain/ -I/usr/src/redhat/BUILD/php-5.0.3/main/ -DPHP_ATOM_INC -I/usr/src/redhat/BUILD/php-5.0.3/include -I/usr/src/redhat/BUILD/php-5.0.3/main -I/usr/src/redhat/BUILD/php-5.0.3 -I/usr/src/redhat/BUILD/php-5.0.3/Zend -I/usr/include/libxml2 -I/usr/include/freetype2 -I/usr/include/imap -I/usr/kerberos/include -I/vrmd/webserver/mhash/include -I/usr/include/mysql -I/usr/include/pspell  -I/usr/src/redhat/BUILD/php-5.0.3/TSRM  -I/usr/kerberos/include  -c main/internal_functions.c -o main/internal_functions.o  && echo > main/internal_functions.lo
/bin/sh /usr/src/redhat/BUILD/php-5.0.3/libtool --silent --preserve-dup-deps --mode=link gcc -export-dynamic -I/usr/kerberos/include  -L/usr/kerberos/lib -L/vrmd/webserver/mhash/lib -L/usr/lib/mysql  -R /usr/kerberos/lib -R /vrmd/webserver/mhash/lib -R /usr/lib/mysql ext/libxml/libxml.lo ext/openssl/openssl.lo ext/openssl/xp_ssl.lo ext/zlib/zlib.lo ext/zlib/zlib_fopen_wrapper.lo ext/bcmath/bcmath.lo ext/bcmath/libbcmath/src/add.lo ext/bcmath/libbcmath/src/div.lo ext/bcmath/libbcmath/src/init.lo ext/bcmath/libbcmath/src/neg.lo ext/bcmath/libbcmath/src/outofmem.lo ext/bcmath/libbcmath/src/raisemod.lo ext/bcmath/libbcmath/src/rt.lo ext/bcmath/libbcmath/src/sub.lo ext/bcmath/libbcmath/src/compare.lo ext/bcmath/libbcmath/src/divmod.lo ext/bcmath/libbcmath/src/int2num.lo ext/bcmath/libbcmath/src/num2long.lo ext/bcmath/libbcmath/src/output.lo ext/bcmath/libbcmath/src/recmul.lo ext/bcmath/libbcmath/src/sqrt.lo ext/bcmath/libbcmath/src/zero.lo ext/bcmath/libbcmath/src/debug.lo ext/bcmath/libbcmath/src/doaddsub.lo ext/bcmath/libbcmath/src/nearzero.lo ext/bcmath/libbcmath/src/num2str.lo ext/bcmath/libbcmath/src/raise.lo ext/bcmath/libbcmath/src/rmzero.lo ext/bcmath/libbcmath/src/str2num.lo ext/bz2/bz2.lo ext/calendar/calendar.lo ext/calendar/dow.lo ext/calendar/french.lo ext/calendar/gregor.lo ext/calendar/jewish.lo ext/calendar/julian.lo ext/calendar/easter.lo ext/calendar/cal_unix.lo ext/ctype/ctype.lo ext/curl/interface.lo ext/curl/multi.lo ext/curl/streams.lo ext/dba/dba.lo ext/dba/dba_cdb.lo ext/dba/dba_db2.lo ext/dba/dba_dbm.lo ext/dba/dba_gdbm.lo ext/dba/dba_ndbm.lo ext/dba/dba_db3.lo ext/dba/dba_db4.lo ext/dba/dba_flatfile.lo ext/dba/dba_inifile.lo ext/dba/dba_qdbm.lo ext/dba/libcdb/cdb.lo ext/dba/libcdb/cdb_make.lo ext/dba/libcdb/uint32.lo ext/dba/libflatfile/flatfile.lo ext/dba/libinifile/inifile.lo ext/dom/php_dom.lo ext/dom/attr.lo ext/dom/document.lo ext/dom/domerrorhandler.lo ext/dom/domstringlist.lo ext/dom/domexception.lo ext/dom/namelist.lo ext/dom/processinginstruction.lo ext/dom/cdatasection.lo ext/dom/documentfragment.lo ext/dom/domimplementation.lo ext/dom/element.lo ext/dom/node.lo ext/dom/string_extend.lo ext/dom/characterdata.lo ext/dom/documenttype.lo ext/dom/domimplementationlist.lo ext/dom/entity.lo ext/dom/nodelist.lo ext/dom/text.lo ext/dom/comment.lo ext/dom/domconfiguration.lo ext/dom/domimplementationsource.lo ext/dom/entityreference.lo ext/dom/notation.lo ext/dom/xpath.lo ext/dom/dom_iterators.lo ext/dom/typeinfo.lo ext/dom/domerror.lo ext/dom/domlocator.lo ext/dom/namednodemap.lo ext/dom/userdatahandler.lo ext/exif/exif.lo ext/ftp/php_ftp.lo ext/ftp/ftp.lo ext/gd/gd.lo ext/gd/gdttf.lo ext/gd/libgd/gd.lo ext/gd/libgd/gd_gd.lo ext/gd/libgd/gd_gd2.lo ext/gd/libgd/gd_io.lo ext/gd/libgd/gd_io_dp.lo ext/gd/libgd/gd_io_file.lo ext/gd/libgd/gd_ss.lo ext/gd/libgd/gd_io_ss.lo ext/gd/libgd/gd_png.lo ext/gd/libgd/gd_jpeg.lo ext/gd/libgd/gdxpm.lo ext/gd/libgd/gdfontt.lo ext/gd/libgd/gdfonts.lo ext/gd/libgd/gdfontmb.lo ext/gd/libgd/gdfontl.lo ext/gd/libgd/gdfontg.lo ext/gd/libgd/gdtables.lo ext/gd/libgd/gdft.lo ext/gd/libgd/gdcache.lo ext/gd/libgd/gdkanji.lo ext/gd/libgd/wbmp.lo ext/gd/libgd/gd_wbmp.lo ext/gd/libgd/gdhelpers.lo ext/gd/libgd/gd_topal.lo ext/gd/libgd/gd_gif_in.lo ext/gd/libgd/xbm.lo ext/gd/libgd/gd_gif_out.lo ext/gettext/gettext.lo ext/iconv/iconv.lo ext/imap/php_imap.lo ext/ldap/ldap.lo ext/mhash/mhash.lo ext/mysql/php_mysql.lo ext/pcre/pcrelib/maketables.lo ext/pcre/pcrelib/get.lo ext/pcre/pcrelib/study.lo ext/pcre/pcrelib/pcre.lo ext/pcre/php_pcre.lo ext/posix/posix.lo ext/pspell/pspell.lo ext/session/session.lo ext/session/mod_files.lo ext/session/mod_mm.lo ext/session/mod_user.lo ext/simplexml/simplexml.lo ext/soap/soap.lo ext/soap/php_encoding.lo ext/soap/php_http.lo ext/soap/php_packet_soap.lo ext/soap/php_schema.lo ext/soap/php_sdl.lo ext/soap/php_xml.lo ext/sockets/sockets.lo ext/spl/php_spl.lo ext/spl/spl_functions.lo ext/spl/spl_engine.lo ext/spl/spl_iterators.lo ext/spl/spl_array.lo ext/spl/spl_directory.lo ext/spl/spl_sxe.lo ext/sqlite/sqlite.lo ext/sqlite/sess_sqlite.lo ext/sqlite/libsqlite/src/opcodes.lo ext/sqlite/libsqlite/src/parse.lo ext/sqlite/libsqlite/src/encode.lo ext/sqlite/libsqlite/src/auth.lo ext/sqlite/libsqlite/src/btree.lo ext/sqlite/libsqlite/src/build.lo ext/sqlite/libsqlite/src/delete.lo ext/sqlite/libsqlite/src/expr.lo ext/sqlite/libsqlite/src/func.lo ext/sqlite/libsqlite/src/hash.lo ext/sqlite/libsqlite/src/insert.lo ext/sqlite/libsqlite/src/main.lo ext/sqlite/libsqlite/src/os.lo ext/sqlite/libsqlite/src/pager.lo ext/sqlite/libsqlite/src/printf.lo ext/sqlite/libsqlite/src/random.lo ext/sqlite/libsqlite/src/select.lo ext/sqlite/libsqlite/src/table.lo ext/sqlite/libsqlite/src/tokenize.lo ext/sqlite/libsqlite/src/update.lo ext/sqlite/libsqlite/src/util.lo ext/sqlite/libsqlite/src/vdbe.lo ext/sqlite/libsqlite/src/attach.lo ext/sqlite/libsqlite/src/btree_rb.lo ext/sqlite/libsqlite/src/pragma.lo ext/sqlite/libsqlite/src/vacuum.lo ext/sqlite/libsqlite/src/copy.lo ext/sqlite/libsqlite/src/vdbeaux.lo ext/sqlite/libsqlite/src/date.lo ext/sqlite/libsqlite/src/where.lo ext/sqlite/libsqlite/src/trigger.lo regex/regcomp.lo regex/regexec.lo regex/regerror.lo regex/regfree.lo ext/standard/array.lo ext/standard/base64.lo ext/standard/basic_functions.lo ext/standard/browscap.lo ext/standard/crc32.lo ext/standard/crypt.lo ext/standard/cyr_convert.lo ext/standard/datetime.lo ext/standard/dir.lo ext/standard/dl.lo ext/standard/dns.lo ext/standard/exec.lo ext/standard/file.lo ext/standard/filestat.lo ext/standard/flock_compat.lo ext/standard/formatted_print.lo ext/standard/fsock.lo ext/standard/head.lo ext/standard/html.lo ext/standard/image.lo ext/standard/info.lo ext/standard/iptc.lo ext/standard/lcg.lo ext/standard/link.lo ext/standard/mail.lo ext/standard/math.lo ext/standard/md5.lo ext/standard/metaphone.lo ext/standard/microtime.lo ext/standard/pack.lo ext/standard/pageinfo.lo ext/standard/parsedate.lo ext/standard/quot_print.lo ext/standard/rand.lo ext/standard/reg.lo ext/standard/soundex.lo ext/standard/string.lo ext/standard/scanf.lo ext/standard/syslog.lo ext/standard/type.lo ext/standard/uniqid.lo ext/standard/url.lo ext/standard/url_scanner.lo ext/standard/var.lo ext/standard/versioning.lo ext/standard/assert.lo ext/standard/strnatcmp.lo ext/standard/levenshtein.lo ext/standard/incomplete_class.lo ext/standard/url_scanner_ex.lo ext/standard/ftp_fopen_wrapper.lo ext/standard/http_fopen_wrapper.lo ext/standard/php_fopen_wrapper.lo ext/standard/credits.lo ext/standard/css.lo ext/standard/var_unserializer.lo ext/standard/ftok.lo ext/standard/sha1.lo ext/standard/user_filters.lo ext/standard/uuencode.lo ext/standard/filters.lo ext/standard/proc_open.lo ext/standard/sunfuncs.lo ext/standard/streamsfuncs.lo ext/standard/http.lo ext/tokenizer/tokenizer.lo ext/wddx/wddx.lo ext/xml/xml.lo ext/xml/compat.lo TSRM/TSRM.lo TSRM/tsrm_strtok_r.lo TSRM/tsrm_virtual_cwd.lo main/main.lo main/snprintf.lo main/spprintf.lo main/php_sprintf.lo main/safe_mode.lo main/fopen_wrappers.lo main/alloca.lo main/php_scandir.lo main/php_ini.lo main/SAPI.lo main/rfc1867.lo main/php_content_types.lo main/strlcpy.lo main/strlcat.lo main/mergesort.lo main/reentrancy.lo main/php_variables.lo main/php_ticks.lo main/network.lo main/php_open_temporary_file.lo main/php_logos.lo main/output.lo main/streams/streams.lo main/streams/cast.lo main/streams/memory.lo main/streams/filter.lo main/streams/plain_wrapper.lo main/streams/userspace.lo main/streams/transports.lo main/streams/xp_socket.lo main/streams/mmap.lo Zend/zend_language_parser.lo Zend/zend_language_scanner.lo Zend/zend_ini_parser.lo Zend/zend_ini_scanner.lo Zend/zend_alloc.lo Zend/zend_compile.lo Zend/zend_constants.lo Zend/zend_dynamic_array.lo Zend/zend_execute_API.lo Zend/zend_highlight.lo Zend/zend_llist.lo Zend/zend_opcode.lo Zend/zend_operators.lo Zend/zend_ptr_stack.lo Zend/zend_stack.lo Zend/zend_variables.lo Zend/zend.lo Zend/zend_API.lo Zend/zend_extensions.lo Zend/zend_hash.lo Zend/zend_list.lo Zend/zend_indent.lo Zend/zend_builtin_functions.lo Zend/zend_sprintf.lo Zend/zend_ini.lo Zend/zend_qsort.lo Zend/zend_multibyte.lo Zend/zend_ts_hash.lo Zend/zend_stream.lo Zend/zend_iterators.lo Zend/zend_interfaces.lo Zend/zend_exceptions.lo Zend/zend_strtod.lo Zend/zend_objects.lo Zend/zend_object_handlers.lo Zend/zend_objects_API.lo Zend/zend_mm.lo Zend/zend_default_classes.lo Zend/zend_reflection_api.lo Zend/zend_execute.lo sapi/cgi/cgi_main.lo sapi/cgi/getopt.lo main/internal_functions.lo -lcrypt -lc-client -lssl -lcrypto -lcrypt -lpspell -lmysqlclient -lmhash -lldap -llber -lcrypt -lpam -lfreetype -lpng -lz -ljpeg -ldb-4.1 -ldb-4.1 -lgdbm -lcurl -lbz2 -lz -lssl -lcrypto -lresolv -lm -ldl -lnsl -lxml2 -lz -lm -lcurl -lssl -lcrypto -lgssapi_krb5 -lkrb5 -lcom_err -lk5crypto -lresolv -ldl -lz -lz -lssl -lcrypto -lssl -lcrypto -lgssapi_krb5 -lkrb5 -lcom_err -lk5crypto -lresolv -ldl -lz -lz -lxml2 -lz -lm -lgssapi_krb5 -lkrb5 -lk5crypto -lcom_err -lxml2 -lz -lm -lxml2 -lz -lm -lcrypt -lxml2 -lz -lm -lcrypt  -o sapi/cgi/php
/usr/lib/gcc-lib/i386-redhat-linux/3.2.3/../../../libc-client.a(osdep.o)(.text+0xab77): In function `ssl_onceonlyinit':
: the use of `tmpnam' is dangerous, better use `mkstemp'
ext/soap/php_encoding.o(.text+0x611): In function `to_zval_string':
: undefined reference to `xmlBufferCreateStatic'
ext/soap/php_encoding.o(.text+0x8bd): In function `to_zval_stringr':
: undefined reference to `xmlBufferCreateStatic'
ext/soap/php_encoding.o(.text+0xb69): In function `to_zval_stringc':
: undefined reference to `xmlBufferCreateStatic'
ext/soap/php_encoding.o(.text+0xfc8): In function `to_xml_string':
: undefined reference to `xmlBufferCreateStatic'
collect2: ld returned 1 exit status
make: *** [sapi/cgi/php] Error 1

Please try using this CVS snapshot:

  http://snaps.php.net/php5-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5-win32-latest.zip

No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

Using the latest snapshot didn't change anything for me.

If I understand the problem correctly, the SOAP extension requires libxml2 version 2.6, the standard 2.5.10 is not enough. The submitter is complaining that configure doesn't give any warning about this.