pgsql: Refactor handling of x86 CPUID instructions

Refactor handling of x86 CPUID instructions

Introduce two helpers for CPUID, pg_cpuid and pg_cpuid_subleaf that wrap
the platform specific __get_cpuid/__cpuid and __get_cpuid_count/__cpuidex
functions.

Additionally, use macros to specify registers names (e.g. EAX) for clarity,
instead of numeric integers into the result array.

Author: Lukas Fittl <lukas@fittl.com>
Suggested-By: John Naylor <john.naylor@postgresql.org>
Discussion: https://postgr.es/m/CANWCAZZ+Crjt5za9YmFsURRMDW7M4T2mutDezd_3s1gTLnrzGQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/be6a7494d2e387d1f5b7a5dcc6c2afcb403188d6

Modified Files
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src/port/pg_cpu_x86.c | 76 ++++++++++++++++++++++++++++++++++-----------------
1 file changed, 51 insertions(+), 25 deletions(-)