pgsql: Centralize detection of x86 CPU features

Centralize detection of x86 CPU features

We now maintain an array of booleans that indicate which features were
detected at runtime. When code wants to check for a given feature,
the array is automatically checked if it has been initialized and if
not, a single function checks all features at once.

Move all x86 feature detection to pg_cpu_x86.c, and move the CRC
function choosing logic to the file where the hardware-specific
functions are defined, consistent with more recent hardware-specific
files in src/port.

Reviewed-by: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
Discussion: https://postgr.es/m/CANWCAZbgEUFw7LuYSVeJ=Tj98R5HoOB1Ffeqk3aLvbw5rU5NTw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/16743db061e431d40522547c6436af6616026caa

Modified Files
--------------
src/include/port/pg_cpu.h | 50 ++++++++++++++++++++++
src/port/pg_cpu_x86.c | 65 +++++++++++-----------------
src/port/pg_crc32c_sse42.c | 32 ++++++++++++++
src/port/pg_popcount_x86.c | 91 ++--------------------------------------
src/tools/pgindent/typedefs.list | 1 +
5 files changed, 112 insertions(+), 127 deletions(-)