This bug exists when PHP is linked with external
static Libtool library and PHP itself is shared.

Compile external support library as static. YAZ in this
example:
 cd yaz-1.8.3
 ./configure --prefix=/usr
 make 
 make install

 cd ../php-4.1.0:
 ./configure --with-apxs=... --with-yaz

and you'd get an output like this:

..
/bin/sh ../libtool --silent --mode=link gcc  -g -O2 -prefer-pic  -o
libZend.la  -ldl -lyaz -lcrypt -lresolv -lm -ldl -lnsl  -lresolv
-lcrypt  zend_language_parser.lo zend_language_scanner.lo
zend_ini_parser.lo zend_ini_scanner.lo zend_alloc.lo zend_compile.lo
zend_c
onstants.lo zend_dynamic_array.lo zend_execute.lo zend_execute_API.lo
zend_highlight.lo zend_llist.lo zend_opcode.lo zend_operators.l
o zend_ptr_stack.lo zend_stack.lo zend_variables.lo zend.lo zend_API.lo
zend_extensions.lo zend_hash.lo zend_list.lo zend_indent.lo z
end_builtin_functions.lo zend_sprintf.lo zend_ini.lo
make[1]: Leaving directory `/home/adam/proj/php-4.1.0/Zend'
...
/bin/sh /home/adam/proj/php-4.1.0/libtool --silent --mode=link gcc  -I.
-I/home/adam/proj/php-4.1.0/ -I/home/adam/proj/php-4.1.0/main
 -I/home/adam/proj/php-4.1.0 -I/home/adam/proj/apache/include
-I/home/adam/proj/php-4.1.0/Zend -I/home/adam/proj/php-4.1.0/ext/mysql/
libmysql -I/home/adam/proj/php-4.1.0/ext/xml/expat  -DLINUX=22
-DUSE_HSREGEX -DUSE_EXPAT -I/home/adam/proj/php-4.1.0/TSRM -g -O2 -pre
fer-pic   -o libphp4.la -rpath /home/adam/proj/php-4.1.0/libs
-avoid-version   stub.lo  Zend/libZend.la sapi/apache/libsapi.la main/l
ibmain.la regex/libregex.la ext/mysql/libmysql.la ext/pcre/libpcre.la
ext/posix/libposix.la ext/session/libsession.la ext/standard/li
bstandard.la ext/xml/libxml.la ext/yaz/libyaz.la TSRM/libtsrm.la -ldl
-lyaz -lcrypt -lresolv -lm -ldl -lnsl -lresolv -lcrypt
/usr/lib/libyaz.a(odr_bool.o): In function `odr_bool':
/home/adam/proj/yaz/odr/odr_bool.c(.text+0x0): multiple definition of
`odr_bool'
Zend/.libs/libZend.al(odr_bool.o)(.text+0x0):/home/adam/proj/yaz/odr/odr
_bool.c: first defined here
/usr/lib/libyaz.a(ber_bool.o): In function `ber_boolean':
[many more multiple symbols]

The log indicates that all YAZ symbols are included twice.
Apparenly the Zend link step includes YAZ verbatim even
though no symbols should be needed to built that.

Fixes:

1) removing /usr/lib/libyaz.la makes it work. Now the
   Zend link step doesn't include YAZ and it works.

2) removing the linkage of yaz from the Zend link step
   obviously makes it work too (and fixes the problem
   for all libraries).

3) build shared YAZ library is a fix too.
   (./configure --enabled-shared for YAZ).

The problem doesn't occur with PHP 4.0.6. It is a problem
with latest CVS (16 Dec 2001).

This problem persists for other libraries than YAZ.
Andrew Sitnikov reports he had trouble with linking of
'-lmm -lmhash' (had to remove them from Zend/Makefile).

If this is a libtool bug and there's no fix for that, my
suggestion would be that Zend doesn't link with
YAZ or other extension libraries. That is the value of
libZend_la_LDFLAGS in Zend/Makefile.am 
should not include @EXTRA_LIBS@.

This bug has been fixed in CVS.