amdgcn: Enable SIMD vectorization of math functions

Calls to vectorized versions of routines in the math library will now
be inserted when vectorizing code containing supported math functions.

2023-03-02  Kwok Cheung Yeung  <kcy@codesourcery.com>
	    Paul-Antoine Arras  <pa@codesourcery.com>

	gcc/
	* builtins.cc (mathfn_built_in_explicit): New.
	* config/gcn/gcn.cc: Include case-cfn-macros.h.
	(mathfn_built_in_explicit): Add prototype.
	(gcn_vectorize_builtin_vectorized_function): New.
	(gcn_libc_has_function): New.
	(TARGET_LIBC_HAS_FUNCTION): Define.
	(TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION): Define.

	gcc/testsuite/
	* gcc.target/gcn/simd-math-1.c: New testcase.
	* gcc.target/gcn/simd-math-2.c: New testcase.

	libgomp/
	* testsuite/libgomp.c/simd-math-1.c: New testcase.