testsuite: aarch64: Add tests for narrowing-arithmetic intrinsics

testsuite: aarch64: Add tests for narrowing-arithmetic intrinsics

Add tests for v[r]addhn_high and v[r]subhn_high Neon intrinsics.
Since these intrinsics are only supported for AArch64, these tests
are restricted to only run on AArch64 targets.

gcc/testsuite/ChangeLog:

2021-03-02  Jonathan Wright  <jonathan.wright@arm.com>

	* gcc.target/aarch64/advsimd-intrinsics/vXXXhn_high.inc:
	New test template.
	* gcc.target/aarch64/advsimd-intrinsics/vaddhn_high.c:
	New test.
	* gcc.target/aarch64/advsimd-intrinsics/vraddhn_high.c:
	New test.
	* gcc.target/aarch64/advsimd-intrinsics/vrsubhn_high.c:
	New test.
	* gcc.target/aarch64/advsimd-intrinsics/vsubhn_high.c:
	New test.