pgsql: Fix compilation of uuid-ossp

Fix compilation of uuid-ossp

This module had a dependency on pgcrypto's md5.c that got removed by
b67b57a.  Instead of the code from pgcrypto, this code can just use the
new cryptohash routines for MD5 as a drop-in replacement, so let's just
do this switch.  This has also the merit to simplify a bit the
compilation of uuid-ossp.

This requires --with-uuid to be reproduced, and I have used e2fs as a
way to reproduce the failure, then test this commit.

Per reports from buildfarm members longfin, florican and sifaka.

Discussion: https://postgr.es/m/X9GToVd3QmWeNvj8@paquier.xyz

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/525e60b7429925d09fce1b5aa0bc2f23cfe6dd18

Modified Files
--------------
configure                     |  4 ++--
configure.ac                  |  4 ++--
contrib/uuid-ossp/Makefile    |  4 ++--
contrib/uuid-ossp/uuid-ossp.c | 16 ++++++++++------
4 files changed, 16 insertions(+), 12 deletions(-)