pgsql: Make EXEC_BACKEND more convenient on Linux and FreeBSD.

Make EXEC_BACKEND more convenient on Linux and FreeBSD.

Try to disable ASLR when building in EXEC_BACKEND mode, to avoid random
memory mapping failures while testing.  For developer use only, no
effect on regular builds.

This has been originally applied as of f3e7806 for v15~, but
recently-added buildfarm member gokiburi tests this configuration on
older branches as well, causing it to fail randomly as ASLR would be
enabled.

Suggested-by: Andres Freund <andres@anarazel.de>
Tested-by: Bossart, Nathan <bossartn@amazon.com>
Discussion: https://postgr.es/m/20210806032944.m4tz7j2w47mant26%40alap3.anarazel.de
Backpatch-through: 12

Branch
------
REL_13_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/1e4fda6da918f734dd6dab67b3ddcaba4c2fecb2

Modified Files
--------------
configure                     |  2 +-
configure.in                  |  1 +
src/bin/pg_ctl/pg_ctl.c       |  4 ++++
src/common/exec.c             | 33 +++++++++++++++++++++++++++++++++
src/include/pg_config.h.in    |  3 +++
src/include/port.h            |  5 +++++
src/test/regress/pg_regress.c |  4 ++++
src/tools/msvc/Solution.pm    |  1 +
8 files changed, 52 insertions(+), 1 deletion(-)