pgsql: Suppress warning about stack_base_ptr with late-model GCC.

Suppress warning about stack_base_ptr with late-model GCC.

GCC 12 complains that set_stack_base is storing the address of
a local variable in a long-lived pointer.  This is an entirely
reasonable warning (indeed, it just helped us find a bug);
but that behavior is intentional here.  We can work around it
by using __builtin_frame_address(0) instead of a specific local
variable; that produces an address a dozen or so bytes different,
in my testing, but we don't care about such a small difference.
Maybe someday a compiler lacking that function will start to issue
a similar warning, but we'll worry about that when it happens.

Patch by me, per a suggestion from Andres Freund.  Back-patch to
v12, which is as far back as the patch will go without some pain.
(Recently-established project policy would permit a back-patch as
far as 9.2, but I'm disinclined to expend the work until GCC 12
is much more widespread.)

Discussion: https://postgr.es/m/3773792.1645141467@sss.pgh.pa.us

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/e0d4123bbcfe6d85eb3130ded4478f2135d116f2

Modified Files
--------------
config/c-compiler.m4                | 22 ++++++++++++++++++++
configure                           | 40 +++++++++++++++++++++++++++++++++++++
configure.in                        |  3 +++
src/backend/postmaster/postmaster.c |  2 +-
src/backend/tcop/postgres.c         | 12 ++++++++++-
src/backend/utils/init/miscinit.c   |  8 ++++++++
src/include/pg_config.h.in          |  3 +++
7 files changed, 88 insertions(+), 2 deletions(-)