AArch64: Add UNSPECV_PATCHABLE_AREA [PR98776]

AArch64: Add UNSPECV_PATCHABLE_AREA [PR98776]

Currently patchable area is at the wrong place on AArch64.  It is placed
immediately after function label, before .cfi_startproc.  This patch
adds UNSPECV_PATCHABLE_AREA for pseudo patchable area instruction and
modifies aarch64_print_patchable_function_entry to avoid placing
patchable area before .cfi_startproc.

gcc/
	PR target/98776
	* config/aarch64/aarch64-protos.h (aarch64_output_patchable_area):
	Declared.
	* config/aarch64/aarch64.c (aarch64_print_patchable_function_entry):
	Emit an UNSPECV_PATCHABLE_AREA pseudo instruction.
	(aarch64_output_patchable_area): New.
	* config/aarch64/aarch64.md (UNSPECV_PATCHABLE_AREA): New.
	(patchable_area): Define.

gcc/testsuite/
	PR target/98776
	* gcc.target/aarch64/pr98776.c: New.
	* gcc.target/aarch64/pr92424-2.c: Adjust pattern.
	* gcc.target/aarch64/pr92424-3.c: Adjust pattern.