pgsql: Introduce --with-ssl={openssl} as a configure option

Introduce --with-ssl={openssl} as a configure option

This is a replacement for the existing --with-openssl, extending the
logic to make easier the addition of new SSL libraries.  The grammar is
chosen to be similar to --with-uuid, where multiple values can be
chosen, with "openssl" as the only supported value for now.

The original switch, --with-openssl, is kept for compatibility.

Author: Daniel Gustafsson, Michael Paquier
Reviewed-by: Jacob Champion
Discussion: https://postgr.es/m/FAB21FC8-0F62-434F-AA78-6BD9336D630A@yesql.se

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/fe61df7f82aa6e0879476146dbe1da9c89b4946b

Modified Files
--------------
configure                                          | 110 +++++++++++++--------
configure.ac                                       |  31 +++---
contrib/Makefile                                   |   2 +-
contrib/pgcrypto/Makefile                          |   4 +-
doc/src/sgml/installation.sgml                     |  23 +++--
doc/src/sgml/pgcrypto.sgml                         |   2 +-
doc/src/sgml/sslinfo.sgml                          |   2 +-
src/Makefile.global.in                             |   2 +-
src/backend/libpq/Makefile                         |   2 +-
src/backend/libpq/hba.c                            |   2 +-
src/common/Makefile                                |   2 +-
src/include/pg_config.h.in                         |   2 +-
src/interfaces/libpq/Makefile                      |   9 +-
src/test/Makefile                                  |   2 +-
src/test/modules/Makefile                          |   2 +-
src/test/modules/ssl_passphrase_callback/Makefile  |   2 +-
.../ssl_passphrase_callback/t/001_testfunc.pl      |   4 +-
src/test/ssl/Makefile                              |   2 +-
src/test/ssl/t/001_ssltests.pl                     |   6 +-
src/test/ssl/t/002_scram.pl                        |   4 +-
src/tools/msvc/Solution.pm                         |   2 +-
src/tools/msvc/config_default.pl                   |   2 +-
22 files changed, 137 insertions(+), 82 deletions(-)