Add missing vector truncmn2 expanders [PR92658]

2020-05-22  Hongtao.liu  <hongtao.liu@intel.com>

gcc/ChangeLog:
	PR target/92658
	* config/i386/sse.md (trunc<pmov_src_lower><mode>2): New expander
	(truncv32hiv32qi2): Ditto.
	(trunc<ssedoublemodelower><mode>2): Ditto.
	(trunc<mode><pmov_dst_3>2): Ditto.
	(trunc<mode><pmov_dst_mode_4>2): Ditto.
	(truncv2div2si2): Ditto.
	(truncv8div8qi2): Ditto.
	(avx512f_<code>v8div16qi2): Renaming from *avx512f_<code>v8div16qi2.
	(avx512vl_<code>v2div2si): Renaming from *avx512vl_<code>v2div2si2.
	(avx512vl_<code><mode>v2<ssecakarnum>qi2): Renaming
	from *avx512vl_<code><mode>v<ssescalarnum>qi2.

gcc/testsuite/ChangeLog:
	* gcc.target/i386/pr92658-avx512f.c: New test.
	* gcc.target/i386/pr92658-avx512vl.c: Ditto.
	* gcc.target/i386/pr92658-avx512bw-trunc.c: Ditto.