pgsql: Refactor some SIMD and popcount macros.

Refactor some SIMD and popcount macros.

This commit does the following:

* Removes TRY_POPCNT_X86_64. We now assume that the required CPUID
intrinsics are available when HAVE_X86_64_POPCNTQ is defined, as we
have done since v16 for meson builds when
USE_SSE42_CRC32C_WITH_RUNTIME_CHECK is defined and since v17 when
USE_AVX512_POPCNT_WITH_RUNTIME_CHECK is defined.

* Moves the MSVC check for HAVE_X86_64_POPCNTQ to configure-time.
This way, we set it for all relevant platforms in one place.

* Moves the #defines for USE_SSE2 and USE_NEON to c.h so that they
can be used elsewhere without including simd.h. Consequently, we
can remove the POPCNT_AARCH64 macro.

* Moves the #includes for pg_bitutils.h to below the system headers
in pg_popcount_{aarch64,x86}.c, since we no longer depend on macros
from pg_bitutils.h to decide which system headers to use.

Reviewed-by: John Naylor <johncnaylorls(at)gmail(dot)com>
Discussion: https://postgr.es/m/aWf_InS1VrbeXAfP%40nathan

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/25dc4850747bb12e871af3589736463edd1d2aa6

Modified Files
--------------
meson.build | 4 +++-
src/include/c.h | 19 +++++++++++++++++++
src/include/port/pg_bitutils.h | 37 +++----------------------------------
src/include/port/simd.h | 17 ++---------------
src/port/pg_bitutils.c | 4 ++--
src/port/pg_popcount_aarch64.c | 8 ++++----
src/port/pg_popcount_x86.c | 8 ++++----
7 files changed, 37 insertions(+), 60 deletions(-)