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(at)anarazel(dot)de>
Tested-by: Bossart, Nathan <bossartn(at)amazon(dot)com>
Discussion: https://postgr.es/m/20210806032944.m4tz7j2w47mant26%40alap3.anarazel.de
Backpatch-through: 12

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/0801345758db44ea8d2da7d8e7d8be2cf3d9bc4e

Modified Files
--------------
configure | 2 +-
configure.ac | 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(-)