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: https://postgr.es/m/17083-a19190d9591946a7@postgresql.org

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/ebc346e5bb72b2a68258f1be8791f2b90191cd38

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