fate: add informative cpu test

libavutil/cpu-test prints raw and effective cpu flags to STDERR. Detected
cpu flags can be useful for debugging fate errors.

No comparison of the result against a expected result since that would
require fate config specific references.
cpu-test: test av_cpu_count

Add CPU count and number threads as informative values for fate.
aarch64: add ',' between assembler macro arguments where missing

llvm's integrated assembler does not accept spaces as macro argument
delimiter when targeting darwin. Using a explicit delimiter is a good
idea in principle since it makes case like 'macro 4 -2' vs 'macro 4 - 2'
clear.
aarch64: use MACH-O const data asm directive in const macro