Re: vectorized CRC on ARM64

Hi,

I happened to do some testing on rpi5 with a 32-bit user space, and when
building with this commit I get these warnings from clang:

config.status: linking src/makefiles/Makefile.linux to src/Makefile.port
pg_crc32c_armv8_choose.c:112:1: warning: unused function
'pg_pmull_available' [-Wunused-function]
112 | pg_pmull_available(void)
| ^~~~~~~~~~~~~~~~~~
1 warning generated.
pg_crc32c_armv8_choose.c:112:1: warning: unused function
'pg_pmull_available' [-Wunused-function]
112 | pg_pmull_available(void)
| ^~~~~~~~~~~~~~~~~~
1 warning generated.
pg_crc32c_armv8_choose.c:112:1: warning: unused function
'pg_pmull_available' [-Wunused-function]
112 | pg_pmull_available(void)
| ^~~~~~~~~~~~~~~~~~
1 warning generated.

I suppose the pg_pmull_available() needs to be if-defed with
USE_PMULL_CRC32C_WITH_RUNTIME_CHECK. That removes the warning for me, at
least.

regards

--
Tomas Vondra