i386: Do not emit mask compares for mode sizes < 16 [PR100445]

i386: Do not emit mask compares for mode sizes < 16 [PR100445]

Recent addition of v*cond* patterns for MMXMODEI modes allows 64bit MMX
modes to enter ix86_expand_sse_cmp. ix86_use_mask_cmp_p was not prepared
to reject mode sizes < 16, resulting in ICE due to unavailability of 64bit
masked PCOM instructions.

2021-05-07  Uroš Bizjak  <ubizjak@gmail.com>

gcc/
	PR target/100445
	* config/i386/i386-expand.c (ix86_use_mask_cmp_p):
	Return false for mode sizes < 16.

gcc/testsuite/

	PR target/100445
	* gcc.target/i386/pr100445-1.c: New test.