Add single_use to simplification (uncond_op + vec_cond -> cond_op).

gcc/ChangeLog:

	PR tree-optimization/104479
	* match.pd (uncond_op + vec_cond -> cond_op): Add single_use
	for the dest of uncond_op.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr104479.c: New test.
	* gcc.target/i386/cond_op_shift_w-1.c: Adjust testcase.