downloaded free sybase-ct libs from link in faq from php site.
unpacked in /sybase-ct
fixed /etc/ld.so.conf & ran ldconfig

then tried to compile php with sybase-ct support (in order to access MSSQL server) as a DSO module:

[root@linux php-4.0.5]# ./configure --with-mysql --with-apxs --enable-sockets --with-oracle=/mnt/ora_syb/ora/app/oracle/product/8.0.5 --with-sybase-ct=/sybase-ct

went fine then ran:
[root@linux php-4.0.5]# make

got the following error:

make[1]: Entering directory `/mnt/ora_syb/php-4.0.5'
/bin/sh /mnt/ora_syb/php-4.0.5/libtool --silent --mode=link gcc  -I. -I/mnt/ora_syb/php-4.0.5/ -I/mnt/ora_syb/php-4.0.5/main -I/mnt/ora_syb/php-4.0.5 -I/usr/include/apache -I/mnt/ora_syb/php-4.0.5/Zend -I/mnt/ora_syb/php-4.0.5/ext/mysql/libmysql -I/mnt/ora_syb/ora/app/oracle/product/8.0.5/rdbms/demo -I/mnt/ora_syb/ora/app/oracle/product/8.0.5/network/public -I/mnt/ora_syb/ora/app/oracle/product/8.0.5/plsql/public -I/sybase-ct/include -I/mnt/ora_syb/php-4.0.5/ext/xml/expat/xmltok -I/mnt/ora_syb/php-4.0.5/ext/xml/expat/xmlparse -I/mnt/ora_syb/php-4.0.5/TSRM  -DLINUX=2 -DEAPI -DUSE_EXPAT -DSUPPORT_UTF8 -DXML_BYTE_ORDER=12 -g -O2   -o libphp4.la -rpath /mnt/ora_syb/php-4.0.5/libs -avoid-version -L/mnt/ora_syb/ora/app/oracle/product/8.0.5/lib -L/sybase-ct/lib  -R /mnt/ora_syb/ora/app/oracle/product/8.0.5/lib -R /sybase-ct/lib stub.lo  Zend/libZend.la sapi/apache/libsapi.la main/libmain.la regex/libregex.la ext/mysql/libmysql.la ext/oracle/liboracle.la ext/pcre/libpcre.la ext/posix/libposix.la ext/session/libsession.la ext/sockets/libsockets.la ext/standard/libstandard.la ext/sybase_ct/libsybase_ct.la ext/xml/libxml.la TSRM/libtsrm.la -lpam -ldl -linsck -lsybtcl -lintl -lcomn -lct -lcs -lclntsh -lpsa -lcore4 -lnlsrtl3 -lm -lnsl -lresolv -lm -ldl -lcrypt -lnsl -lresolv
collect2: ld terminated with signal 11 [Segmentation fault], core dumped
/sybase-ct/lib/libct.a(ctconpr.o)(.text+0x5ac): undefined reference to `comn_loc_copy'
make[1]: *** [libphp4.la] Error 1
make[1]: Leaving directory `/mnt/ora_syb/php-4.0.5'
make: *** [all-recursive] Error 1

N.B.
previous run witout sybase-ct support went fine!