The Makefile is missing '-liconv' when linking, manually adding it to "EXTRA_LIBS" solves the linking problem, but there seems to be some kind of problem with the autoconf...
(The problem also exists in php4-STABLE-200304190130 )

This is my config.
Solaris8 i386 
Sun Forte 6 update1 (5.2) compiler
libiconv-1.8 installed with /usr/local as prefix
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setenv CC cc
setenv CXX CC
setenv CFLAGS "-xCC -xO3"
setenv CXXFLAGS "-xO3"
./configure --with-apxs --with-mysql=/usr/local/mysql \
--with-imap=../mail/uw-imap/imap-2001a --with-openssl \
--with-imap-ssl --with-gettext --with-xml --with-mcrypt \
--with-zlib --enable-calendar --with-mm --with-dom \
--with-dom-xslt --enable-mime-magic --with-iconv \
--enable-mbstring --enable-ftp
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Some lines from config.log
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configure:33590: checking for iconv support
configure:33641: checking for iconv
configure:34040: checking if iconv supports errno
configure:34076: cc -o conftest -xCC -xO3  -I$(top_builddir)/Zend -I/usr/local/s
sl/include -I/usr/local/include/libxml2 -I/usr/local/include  -D_POSIX_PTHREAD_S
EMANTICS -DSOLARIS2=280 -DMOD_SSL=208114 -DEAPI -DEAPI_MM -DUSE_EXPAT  -R/usr/uc
blib -L/usr/ucblib -R/usr/local/ssl/lib -L/usr/local/ssl/lib -R/usr/local/lib -L
/usr/local/lib conftest.c -lintl -lxsltbreakpoint -lxml2 -lxslt -lz -lz -lcrypt 
-lssl -lcrypto -lresolv -lm -ldl -lnsl -lsocket  -lcrypt -lxml2 -lz -lm -lsocket
 -lnsl 1>&5
"conftest.c", line 1: warning: 34045 is invalid in #line directive
"configure", line 34062: warning: improper pointer/integer combination: op "="
Undefined                       first referenced
 symbol                             in file
libiconv_open                       conftest.o
libiconv_close                      conftest.o
ld: fatal: Symbol referencing errors. No output written to conftest
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Last lines of output from 'make'
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/bin/bash libtool --silent --mode=link cc -export-dynamic -xCC -xO3  -avoid-version -module -L/usr/ucblib -L/usr/local/ssl/lib -L/usr/local/lib -L/home/hson/src/mail/uw-imap/imap-2001a/lib -L/usr/local/mysql/lib/mysql  -R /usr/ucblib -R /usr/local/ssl/lib -R /usr/local/lib -R /home/hson/src/mail/uw-imap/imap-2001a/lib -R /usr/local/mysql/lib/mysql ext/zlib/zlib.lo ext/zlib/zlib_fopen_wrapper.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/domxml/php_domxml.lo ext/ftp/php_ftp.lo ext/ftp/ftp.lo ext/gettext/gettext.lo ext/iconv/iconv.lo ext/imap/php_imap.lo ext/mbstring/mbfilter_ja.lo ext/mbstring/mbfilter_cn.lo ext/mbstring/mbfilter_tw.lo ext/mbstring/mbfilter_kr.lo ext/mbstring/mbfilter_ru.lo ext/mbstring/mbfilter.lo ext/mbstring/mbstring.lo ext/mbstring/mbregex.lo ext/mbstring/php_mbregex.lo ext/mbstring/html_entities.lo ext/mbstring/php_unicode.lo ext/mcrypt/mcrypt.lo ext/mime_magic/mime_magic.lo ext/mysql/php_mysql.lo ext/openssl/openssl.lo ext/overload/overload.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/session/session.lo ext/session/mod_files.lo ext/session/mod_mm.lo ext/session/mod_user.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/aggregation.lo ext/standard/sha1.lo ext/tokenizer/tokenizer.lo ext/xml/xml.lo ext/xml/expat/xmlparse.lo ext/xml/expat/xmlrole.lo ext/xml/expat/xmltok.lo regex/regcomp.lo regex/regexec.lo regex/regerror.lo regex/regfree.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_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/streams.lo main/network.lo main/php_open_temporary_file.lo main/php_logos.lo main/output.lo main/memory_streams.lo main/user_streams.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_execute.lo sapi/cli/php_cli.lo sapi/cli/getopt.lo main/internal_functions_cli.lo -lcrypto -lssl -lc-client -lmm -lmysqlclient -lmcrypt -lltdl -lcrypt -lpam -lintl -lxsltbreakpoint -lxml2 -lxslt -lz -lz -lcrypt -lssl -lcrypto -lresolv -lm -ldl -lnsl -lsocket -lcrypt -lxml2 -lz -lm -lsocket -lnsl  -o sapi/cli/php
Undefined                       first referenced
 symbol                             in file
libiconv                            ext/iconv/iconv.lo
libiconv_open                       ext/iconv/iconv.lo
libiconv_close                      ext/iconv/iconv.lo
ld: fatal: Symbol referencing errors. No output written to sapi/cli/php
*** Error code 1
make: Fatal error: Command failed for target `sapi/cli/php'
hson@solpc-01 1:49  ~/src/mail/php-4.3/php-4.3.1 >
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