Sorry ! Did not enter a password in bug-report 12825 (so i am not able to submit a direct reply), anyway ...
I started compiling php4.0.6 with:

./configure --prefix=/usr --bindir=/usr/bin --libdir=/usr/lib --with-config-file-path=/etc --with-exec-dir=%{libdir}/php/bin --with-pgsql=/usr --with-mysql=/usr --with-gd=yes --with-tiff-dir=/usr --with-jpeg-dir=/usr --with-png-dir=/usr --with-xpm-dir=/usr/X11R6 --with-pdflib=/usr --with-ldap=yes --with-imap=yes --with-imap-ssl --with-zlib=yes --with-bz2 --with-xml --with-ttf --with-t1lib --with-mcal=/usr/include/mcal/ --with-sablot --with-readline --with-ftp --with-ndbm --with-gdbm --with-mcrypt --with-gettext --with-curl --with-mm --with-gd=yes --with-qtdom=/usr/lib/qt2/ --enable-versioning --enable-yp --enable-bcmath --enable-trans-sid --enable-inline-optimization --enable-track-vars --enable-magic-quotes --enable-safe-mode --enable-sockets --enable-sysvsem --enable-sysvshm --enable-shmop --enable-calendar --enable-exif --enable-ftp --enable-memory-limit --enable-wddx --enable-filepro --enable-dbase --enable-ctype --enable-debug --enable-force-cgi-redirect --enable-discard-path --enable-sigchild --enable-gd-imgstrttf --with-openssl --with-swf=./usr --with-apxs=/usr/sbin/apxs --with-sybase-ct=/usr/local/freetds

And once again, all worked fine, all but starting apache's http daemon.
Nevertheless, i could not find anything describing the "undefined symbol" error in general.