Commit 9385aaa84851 ("[sancov] Fix PR33732") added zeroext to
__sanitizer_cov_trace(_const)?_cmp parameters for x86_64 only,
however, it is useful on other targets, in particular, on SystemZ: it
Therefore, use it on all targets. This is safe: if target ABI does not
require zero extension for a particular parameter, zeroext is simply
ignored. A similar change has been implemeted as part of commit
3bc439bdff8b ("[MSan] Add instrumentation for SystemZ"), and there were
no problems with it.