/var/log/httpd/error_log:
PHP Warning:  Invalid library (maybe not a PHP library) 'pgsql.so'  in Unknown on line 0

./configure i686-pld-linux --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib --libexecdir=/usr/libexec --localstatedir=/usr/var --sharedstatedir=/usr/com --mandir=/usr/share/man --infodir=/usr/share/info --with-apxs=/usr/sbin/apxs --with-config-file-path=/etc/httpd --with-exec-dir=/usr/bin --disable-debug --enable-magic-quotes --enable-shared --enable-track-vars --enable-safe-mode --enable-trans-sid --enable-sysvsem --enable-sysvshm --enable-xml=shared --with-zlib --with-regex=system --with-gettext --with-mysql --with-dbase --with-filepro --with-ftp --with-hyperwave --with-java --with-pdflib --with-pgsql=shared,/usr

php.ini:
extension_dir   =       /usr/lib/apache/php/
extension=pgsql.so

ls -l /usr/lib/apache/php/pgsql.so:
-rwxr-xr-x    1 root     root        24176 mar 30 18:40 /usr/lib/apache/php/pgsql.so

file /usr/lib/apache/php/pgsql.so:
/usr/lib/apache/php/pgsql.so: ELF 32-bit LSB shared object, Intel 80386, version 1, stripped

System:
Apache 1.3.12 (./configure --prefix=/usr --sysconfdir=/etc/httpd --includedir=/usr/include/apache --sbindir=/usr/sbin --libexecdir=/usr/lib/apache --datadir=/home/httpd --localstatedir=/var --runtimedir=/var/run --logfiledir=/var/log/httpd --with-layout=PLD --without-confadjust --enable-module=all --enable-shared=max --proxycachedir=/var/cache/apache --with-perl=/usr/bin/perl --enable-suexec --suexec-caller=http --suexec-uidmin=500 --suexec-gidmin=500 --disable-rule=WANTHSREGEX --enable-rule=EAPI)

Linux matylda 2.2.14 #2 Fri Mar 17 00:58:09 CET 2000 i686 pld

glibc 2.1.3, gcc 2.95.2