[AArch64, PATCH] Improve Neon store of zero

Committed on behalf of Jackson Woodruff.

---
gcc/

	* config/aarch64/constraints.md (Umq): New constraint.
	* config/aarch64/aarch64-simd.md (*aarch64_simd_mov<mode>):
	Change to use Umq.
	(mov<mode>): Update condition.

gcc/testsuite/

	* gcc.target/aarch64/simd/vect_str_zero.c: Update testcase.

From-SVN: r252387