Fix ICE of unrecognizable insn.

Fix ICE of unrecognizable insn.

The new added splitter will generate

(insn 58 56 59 2 (set (reg:V4HI 20 xmm0 [129])
        (vec_duplicate:V4HI (reg:HI 22 xmm2 [123]))) "testcase.c":16:21 -1

But we only have

(define_insn "*vec_dupv4hi"
  [(set (match_operand:V4HI 0 "register_operand" "=y,Yw")
	(vec_duplicate:V4HI
	  (truncate:HI
	    (match_operand:SI 1 "register_operand" "0,Yw"))))]

The patch add patterns for V4HI and V2HI.

gcc/ChangeLog:

	PR target/112532
	* config/i386/mmx.md (*vec_dup<mode>): Extend for V4HI and
	V2HI.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr112532.c: New test.