vect: support direct conversion under x86-64-v3.

vect: support direct conversion under x86-64-v3.

gcc/ChangeLog:

	PR target/107432
	* config/i386/i386-expand.cc (ix86_expand_trunc_with_avx2_noavx512f):
	New function for generate a series of suitable insn.
	* config/i386/i386-protos.h (ix86_expand_trunc_with_avx2_noavx512f):
	Define new function.
	* config/i386/sse.md: Extend trunc<mode><mode>2 for x86-64-v3.
	(ssebytemode) Add V8HI.
	(PMOV_DST_MODE_2_AVX2): New mode iterator.
	(PMOV_SRC_MODE_3_AVX2): Ditto.
	* config/i386/mmx.md
	(trunc<mode><mmxhalfmodelower>2): Ditto.
	(avx512vl_trunc<mode><mmxhalfmodelower>2): Ditto.
	(truncv2si<mode>2): Ditto.
	(avx512vl_truncv2si<mode>2): Ditto.
	(mmxbytemode): New mode attr.

gcc/testsuite/ChangeLog:

	PR target/107432
	* gcc.target/i386/pr107432-8.c: New test.
	* gcc.target/i386/pr107432-9.c: Ditto.
	* gcc.target/i386/pr92645-4.c: Modify test.