arm: improve tests for vqdmlsdhxq*

arm: improve tests for vqdmlsdhxq*

gcc/testsuite/ChangeLog:

	* gcc.target/arm/mve/intrinsics/vqdmlsdhxq_m_s16.c: Use
	check-function-bodies instead of scan-assembler checks.  Use
	extern "C" for C++ testing.
	* gcc.target/arm/mve/intrinsics/vqdmlsdhxq_m_s32.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vqdmlsdhxq_m_s8.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vqdmlsdhxq_s16.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vqdmlsdhxq_s32.c: Likewise.
	* gcc.target/arm/mve/intrinsics/vqdmlsdhxq_s8.c: Likewise.