pgsql: Remove --disable-thread-safety and related code.

Remove --disable-thread-safety and related code.

All supported computers have either POSIX or Windows threads, and we no
longer have any automated testing of --disable-thread-safety.  We define
a vestigial ENABLE_THREAD_SAFETY macro to 1 in ecpg_config.h in case it
is useful, but we no longer test it anywhere in PostgreSQL code, and
associated dead code paths are removed.

The Meson and perl-based Windows build scripts never had an equivalent
build option.

Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/CA%2BhUKGLtmexrpMtxBRLCVePqV_dtWG-ZsEbyPrYc%2BNBB2TkNsw%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/68a4b58eca032916e2aad78d63f717dcb147e906

Modified Files
--------------
configure                                          | 54 ++--------------
configure.ac                                       | 26 ++------
doc/src/sgml/installation.sgml                     | 13 ----
meson.build                                        | 11 ----
src/Makefile.global.in                             |  1 -
src/bin/pgbench/pgbench.c                          | 22 +------
src/include/pg_config.h.in                         |  4 --
src/interfaces/ecpg/ecpglib/connect.c              | 40 ------------
src/interfaces/ecpg/ecpglib/descriptor.c           | 10 ---
src/interfaces/ecpg/ecpglib/ecpglib_extern.h       |  2 -
src/interfaces/ecpg/ecpglib/execute.c              |  2 -
src/interfaces/ecpg/ecpglib/memory.c               |  7 ---
src/interfaces/ecpg/ecpglib/misc.c                 | 47 --------------
src/interfaces/ecpg/include/ecpg-pthread-win32.h   |  3 -
src/interfaces/ecpg/include/ecpg_config.h.in       |  5 +-
src/interfaces/ecpg/include/ecpglib.h              |  2 -
src/interfaces/ecpg/include/meson.build            |  3 +-
src/interfaces/ecpg/test/expected/thread-alloc.c   | 43 ++++++-------
.../ecpg/test/expected/thread-descriptor.c         | 22 +++----
src/interfaces/ecpg/test/expected/thread-prep.c    | 71 ++++++++++------------
src/interfaces/ecpg/test/expected/thread-thread.c  | 63 ++++++++-----------
.../ecpg/test/expected/thread-thread_implicit.c    | 63 ++++++++-----------
src/interfaces/ecpg/test/thread/alloc.pgc          |  9 ---
src/interfaces/ecpg/test/thread/descriptor.pgc     |  8 +--
src/interfaces/ecpg/test/thread/prep.pgc           |  9 ---
src/interfaces/ecpg/test/thread/thread.pgc         |  9 ---
.../ecpg/test/thread/thread_implicit.pgc           |  9 ---
src/interfaces/libpq/Makefile                      |  5 +-
src/interfaces/libpq/fe-connect.c                  |  4 --
src/interfaces/libpq/fe-exec.c                     |  4 --
src/interfaces/libpq/fe-print.c                    | 13 +---
src/interfaces/libpq/fe-secure-openssl.c           | 17 +-----
src/interfaces/libpq/fe-secure.c                   | 26 +-------
src/interfaces/libpq/legacy-pqsignal.c             |  4 +-
src/interfaces/libpq/libpq-int.h                   |  9 +--
src/makefiles/meson.build                          |  1 -
src/tools/msvc/Solution.pm                         |  3 +-
src/tools/msvc/ecpg_regression.proj                |  2 +-
38 files changed, 137 insertions(+), 509 deletions(-)