Eliminate redundant vpextrq/vpinsrq when move TI to V4SI.

Eliminate redundant vpextrq/vpinsrq when move TI to V4SI.

r14-1902-g96c3539f2a3813 split TImode move with 2 DImode move, it's
supposed to optimize TImode in parameter/return since accoring to
psABI it's stored into 2 general registers.

But when TImode is not in parameter/return, it could create redundancy
in the PR.

The patch add a splitter to handle that.

.i.e.
(insn 10 9 14 2 (set (subreg:V2DI (reg:V4SI 98 [ <retval> ]) 0)
		     (vec_concat:V2DI (subreg:DI (reg:TI 101) 0)
			 (subreg:DI (reg:TI 101) 8)))
			 8442 {vec_concatv2di}
			(expr_list:REG_DEAD (reg:TI 101)

gcc/ChangeLog:

	PR target/121274
	* config/i386/sse.md (*vec_concatv2di_0): Add a splitter
	before it.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr121274.c: New test.

(cherry picked from commit 6a466839340dce3b596b3ae5ce85bd05a067ae00)