pgsql: Remove configurability of PPC spinlock assembly code.

Remove configurability of PPC spinlock assembly code.

Assume that we can use LWARX hint flags and the LWSYNC instruction
on any PPC machine. The check on the assembler's behavior was only
needed for Apple's old assembler, which is no longer of interest
now that we've de-supported all PPC-era versions of macOS (thanks
to them not having clock_gettime()). Also, given an up-to-date
assembler these instructions work even on Apple's old hardware.
It seems quite unlikely that anyone would be interested in running
current Postgres on PPC hardware that's so old as to not have
these instructions.

Hence, rip out associated configure test and manual configuration
options, and just use the modernized instructions all the time.
Also, update atomics/arch-ppc.h to use these instructions as well.
(It was already using LWSYNC unconditionally in another place,
providing further proof that nobody is using PG on hardware old
enough to have a problem with that.)

Discussion: https://postgr.es/m/166622.1660323391@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8ded65682bee2a1c04392a88e0df0f4fc7552623

Modified Files
--------------
configure | 34 +------------------------------
configure.ac | 13 +-----------
src/include/pg_config.h.in | 3 ---
src/include/pg_config_manual.h | 26 ------------------------
src/include/port/atomics/arch-ppc.h | 40 ++++++++++++++++++-------------------
src/include/storage/s_lock.h | 24 ++++------------------
src/tools/msvc/Solution.pm | 1 -
7 files changed, 26 insertions(+), 115 deletions(-)