os: detect PMULL support before enabling accelerated crc32c on ARM

os: detect PMULL support before enabling accelerated crc32c on ARM

Issue #1239 shows a crash on a FUJITSU/A64FX ARM platform at the
following line:

crc/crc32c-arm64.c:
 64                 t1 = (uint64_t)vmull_p64(crc1, k2);

On armv8 PMULL crypto instructions like vmull_p64 are defined as
optional (see
https://github.com/google/crc32c/pull/6#issuecomment-328713398 and
https://github.com/dotnet/runtime/issues/35143#issuecomment-617263508 ).

Avoid the crash by gating use of the hardware accelerated ARM crc32c
path behind runtime detection of PMULL.

Fixes: https://github.com/axboe/fio/issues/1239

Signed-off-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>