aarch64: Fix FEAT_PCDPHINT for C++

aarch64: Fix FEAT_PCDPHINT for C++

This patch rewrites the _Generic in arm_acle.h into a resolve_overloaded_builtin.
The reason for this was the lack of support in C++ for _Generic.

gcc/ChangeLog:

	* config/aarch64/aarch64-builtins.cc
	(enum aarch64_builtins): Add ptr and generic variants.
	(aarch64_init_pcdphint_builtins): Likewise.
	(aarch64_general_expand_builtin): Add ptr variant.
	(aarch64_resolve_overloaded_builtin_stshh): Function to handle
	overloaded atomic_store_with_stshh.
	(aarch64_resolve_overloaded_builtin_general): Add call to stshh function.
	* config/aarch64/aarch64-c.cc
	(aarch64_resolve_overloaded_builtin): Allow fndecl to return.
	* config/aarch64/arm_acle.h
	(__atomic_store_with_stshh): Remove __Generic.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/atomic_store_with_stshh.c: Testcase change.
	* g++.target/aarch64/atomic_store_with_stshh.C: New test.