pgsql: Require compiler barrier support.

Require compiler barrier support.

Previously we had a fallback implementation of pg_compiler_barrier()
that called an empty function across a translation unit boundary so the
compiler couldn't see what it did. That shouldn't be needed on any
current systems, and might not even work with a link time optimizer.
Since we now require compiler-specific knowledge of how to implement
atomics, we should also know how to implement compiler barriers on a
hypothetical new system.

Reviewed-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Suggested-by: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/721bf39a-ed8a-44b0-8b8e-be3bd81db748%40technowledgy.de
Discussion: https://postgr.es/m/3351991.1697728588%40sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a011dc399cc82be07326c89c926bd5880160b1ba

Modified Files
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src/backend/port/atomics.c | 8 --------
src/include/port/atomics.h | 3 +++
src/include/port/atomics/fallback.h | 15 ---------------
3 files changed, 3 insertions(+), 23 deletions(-)