testsuite: aarch64: Add tests for vmull_high intrinsics

testsuite: aarch64: Add tests for vmull_high intrinsics

Add tests for vmull_high_* Neon intrinsics. Since these intrinsics
are only supported for AArch64, these tests are restricted to only
run on AArch64 targets.

gcc/testsuite/ChangeLog:

2021-01-29  Jonathan Wright  <jonathan.wright@arm.com>

	* gcc.target/aarch64/advsimd-intrinsics/vmull_high.c:
	New test.
	* gcc.target/aarch64/advsimd-intrinsics/vmull_high_lane.c:
	New test.
	* gcc.target/aarch64/advsimd-intrinsics/vmull_high_laneq.c:
	New test.
	* gcc.target/aarch64/advsimd-intrinsics/vmull_high_n.c:
	New test.