Compile error on the aarch64 platform: Missing asm/hwcap.h

Hi,

Compile error on CentOS Linux release 7.6.1810 (AltArch) with the message “‘HWCAP_CRC32’ undeclared”.

Relevant code from discussion: https://www.postgresql.org/message-id/4496616.iHFcN1HehY%40portable-bastien
It mentions: "It doesn't look like I need to include <asm/hwcap.h> from Bastien's
original message, because <sys/auxv.h> pulls in <bits/hwcap.h>
already."

However, the bits/hwcap.h file included with glibc in CentOS 7.6 lacks these symbol definitions (the file is nearly empty). This file appears to be an internal glibc dependency, so it's preferable to directly use asm/hwcap.h for the required symbol definitions.

After modifying the code to add `include <asm/hwcap.h>`, the compilation succeeded.