Fix pg_crc32c_armv8_choose.c to build with ancient glibc releases.

Fix pg_crc32c_armv8_choose.c to build with ancient glibc releases.

If you go back as far as the RHEL7 era, <sys/auxv.h> does not provide
the HWCAPxxx macros needed with elf_aux_info or getauxval, so you need
to get those from the kernel header <asm/hwcap.h> instead.  We knew
that for the 32-bit case but failed to extrapolate to the 64-bit case.
Oversight in commit aac831caf.

Reported-by: GaoZengqi <pgf00a@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAFmBtr3Av62-jBzdhFkDHXJF9vQmNtSnH2upwODjnRcsgdTytw@mail.gmail.com
Backpatch-through: 18