docs: Fix wording describing the hwaddress sanitizer
The original documentation added to mention the clash between
-fsanitize=address and -fsanitize=hwaddress used confusing wording trying
to say that -fsanitize=hwaddress is only available on AArch64.
It read as if -fsanitize=address were only supported on AArch64.
This patch fixes that wording by being more explicit.