targethooks: Change SAME_FUNCTION_VERSIONS hook to support checking mergeability

targethooks: Change SAME_FUNCTION_VERSIONS hook to support checking mergeability

This changes the hook to support checking version mergeability for cases
where the version strings do imply the same version, but are conflicting
in some other way so cannot be merged.

This is a change required for adding priority version support in aarch64.

gcc/ChangeLog:

	* target.def (TARGET_OPTION_SAME_FUNCTION_VERSIONS): Update
	documentation.
	* tree.cc (disjoint_version_decls): Change for new NULL parameter
	to same_function_versions.
	(diagnose_versioned_decls): Update to pass diagnostic location to
	same_function_versions.
	* doc/tm.texi: Regenerate.
	* config/aarch64/aarch64.cc (aarch64_same_function_versions):
	Update hook impl for new arguments.
	* config/riscv/riscv.cc (riscv_same_function_versions): Update
	hook impl for new arguments.
	* config/loongarch/loongarch.cc
	(loongarch_same_function_versions): Likewise
	* hooks.cc (hook_stringslice_stringslice_unreachable): Changed
	to...
	(hook_stringslice_consttree_stringslice_consttree_unreachable):
	...this and add extra arguments.
	* hooks.h (hook_stringslice_stringslice_unreachable): Changed
	to...
	(hook_stringslice_consttree_stringslice_consttree_unreachable):
	and add extra arguments.