Allow the ldap extension to be compiled with Oracle's LDAP

Allow the ldap extension to be compiled with Oracle's LDAP
implementation, if desired.  Note the implementations differ so you
will see different ldap behavior.

The patch allows configuration similar to:
--with-ldap=$HOME/instantclient --with-oci8=instantclient,$HOME/instantclient

The patch doesn't support configuration similar to:
--with-ldap --with-oci8=instantclient,$HOME/instantclient
since this would try and mix the default LDAP and Oracle LDAP
implementations.

This patch closes out bug #61450 and the associated github PR.

Regardless of this patch, my recommended way to install both OCI8 and
ldap extensions is to statically configure PHP with ldap, and then add
OCI8 as a shared extension from PECL.