i386: Fix emissing of __builtin_cpu_supports.

	PR target/103661

gcc/ChangeLog:

	* config/i386/i386-builtins.c (fold_builtin_cpu): Compare to 0
	as API expects that non-zero values are returned (do that
	it mask == 31).
	For "avx512vbmi2" argument, we return now 1 << 31, which is a
	negative integer value.