pgsql: pgcrypto: Make it possible to disable built-in crypto

pgcrypto: Make it possible to disable built-in crypto

When using OpenSSL and/or the underlying operating system in FIPS
mode no non-FIPS certified crypto implementations should be used.
While that is already possible by just not invoking the built-in
crypto in pgcrypto, this adds a GUC which prohibit the code from
being called. This doesn't change the FIPS status of PostgreSQL
but can make it easier for sites which target FIPS compliance to
ensure that violations cannot occur.

Author: Daniel Gustafsson <daniel(at)yesql(dot)se>
Author: Joe Conway <mail(at)joeconway(dot)com>
Reviewed-by: Joe Conway <mail(at)joeconway(dot)com>
Reviewed-by: Peter Eisentraut <peter(at)eisentraut(dot)org>
Reviewed-by: Hayato Kuroda <kuroda(dot)hayato(at)fujitsu(dot)com>
Discussion: https://postgr.es/m/16b4a157-9ea1-44d0-b7b3-4c85df5de97b@joeconway.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/035f99cbebe5ffcaf52f8370394446cd59621ab7

Modified Files
--------------
contrib/pgcrypto/expected/crypt-des.out | 7 ++++++
contrib/pgcrypto/openssl.c | 26 ++++++++++++++++++++++
contrib/pgcrypto/pgcrypto.c | 31 +++++++++++++++++++++++++++
contrib/pgcrypto/px-crypt.c | 4 ++++
contrib/pgcrypto/px.h | 9 ++++++++
contrib/pgcrypto/sql/crypt-des.sql | 6 ++++++
doc/src/sgml/pgcrypto.sgml | 38 +++++++++++++++++++++++++++++++++
7 files changed, 121 insertions(+)