aarch64: Fix memtag intrinsic availability

The availability of memtag intrinsics and data types were determined
solely by the globally specified architecture features, which did not
reflect any changes specified in target pragmas or attributes.

This patch removes the initialisation-time guards for the intrinsics,
and replaces them with checks at use time. It also removes the macro
indirection from the header file - this simplifies the header, and
allows the missing extension error reporting to find the user-facing
intrinsic names.

gcc/ChangeLog:

	PR target/112108
	* config/aarch64/aarch64-builtins.cc (aarch64_init_memtag_builtins):
	Define intrinsic names directly.
	(aarch64_general_init_builtins): Move memtag intialisation...
	(handle_arm_acle_h): ...to here, and remove feature check.
	(aarch64_general_check_builtin_call): Check memtag intrinsics.
	* config/aarch64/arm_acle.h (__arm_mte_create_random_tag)
	(__arm_mte_exclude_tag, __arm_mte_ptrdiff)
	(__arm_mte_increment_tag, __arm_mte_set_tag, __arm_mte_get_tag):
	Remove.

gcc/testsuite/ChangeLog:

	PR target/112108
	* gcc.target/aarch64/acle/memtag_guard-1.c: New test.
	* gcc.target/aarch64/acle/memtag_guard-2.c: New test.
	* gcc.target/aarch64/acle/memtag_guard-3.c: New test.
	* gcc.target/aarch64/acle/memtag_guard-4.c: New test.