pgsql: Fix busted test for ldap_initialize.

Fix busted test for ldap_initialize.

Sigh ... I was expecting AC_CHECK_LIB to do something it didn't,
namely update LIBS. This led to not finding ldap_initialize.
Fix by moving the probe for ldap_initialize. In some sense this
is more correct anyway, since (at least for now) we care about
whether ldap_initialize exists in libldap not libldap_r.

Per buildfarm member elver and local testing.

Discussion: /messages/by-id/17083-a19190d9591946a7@postgresql.org

Branch
------
REL_11_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/946f62f2fb828630ba0cf56adea34fa7d0fd22d9

Modified Files
--------------
configure | 23 ++++++++++++-----------
configure.in | 3 ++-
2 files changed, 14 insertions(+), 12 deletions(-)