pgsql: For all ppc compilers, implement compare_exchange and fetch_add

For all ppc compilers, implement compare_exchange and fetch_add with asm.

This is more like how we handle s_lock.h and arch-x86.h.

Reviewed by Tom Lane.

Discussion: https://postgr.es/m/20191005173400.GA3979129@rfd.leadboat.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/30ee5d17c20dbb282a9952b3048d6ad52d56c371

Modified Files
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configure                              |  40 ++++++
configure.in                           |  20 +++
src/include/pg_config.h.in             |   3 +
src/include/port/atomics.h             |  11 +-
src/include/port/atomics/arch-ppc.h    | 231 +++++++++++++++++++++++++++++++++
src/include/port/atomics/generic-xlc.h | 142 --------------------
src/tools/pginclude/cpluspluscheck     |   1 -
src/tools/pginclude/headerscheck       |   1 -
8 files changed, 298 insertions(+), 151 deletions(-)