aarch64: Fix memtag builtins vs GC [PR108174]

The memtag builtins were being GC'ed away so we end up
with a crash sometimes (maybe even wrong code).
This fixes that issue by adding GTY on the variable/struct
aarch64_memtag_builtin_data.

Committed as obvious after a build/test for aarch64-linux-gnu.

	PR target/108174

gcc/ChangeLog:

	* config/aarch64/aarch64-builtins.cc (aarch64_memtag_builtin_data): Make
	static and mark with GTY.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/acle/memtag_4.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>