Fix searching for libraries like LDAP

The checks for things like ext/ldap will assume libraries are in ./lib,
and not lib64 like they are on many multilib systems, Gentoo included.

Gross that we're hardcoding it, but we should also probably convert
ldap to pkg-config sometime. That may require getting rid of Oracle or
Solaris LDAP support though.

Author: NattyNarwhal

.github/actions/configure-gentoo/action.yml

@@ -16,6 +16,7 @@ runs:
         ./configure \
           --enable-option-checking=fatal \
           --prefix=/usr \
+          --with-libdir=lib64 \
           --enable-phpdbg \
           --enable-fpm \
           --with-pdo-mysql=mysqlnd \