Revert "For all ppc compilers, implement pg_atomic_fetch_add_ with inline asm."
This reverts commit
e7ff59686eacf5021fb84be921116986c3828d8a. It
defined pg_atomic_fetch_add_u32_impl() without defining
pg_atomic_compare_exchange_u32_impl(), which is incompatible with
src/include/port/atomics/fallback.h. Per buildfarm member prairiedog.
Discussion: https://postgr.es/m/7517.
1568470247@sss.pgh.pa.us