AArch64: Treat pauth ops as nops on non-pauth systems

AArch64: Treat pauth ops as nops on non-pauth systems

Running an address signed binary through GDB on a non pauth system
gives the following error:
Call Frame Instruction op 45 in vendor extension space is not handled on this architecture.

Instead GDB should ignore the op, treating it as a nop.

Add test case for pauth binaries, regardless of whether the target
supports it.

gdb/ChangeLog:

	* aarch64-tdep.c (aarch64_execute_dwarf_cfa_vendor_op): Treat
	DW_CFA_AARCH64_negate_ra_state as nop on non pauth targets.

gdb/testsuite/ChangeLog:

	* gdb.arch/aarch64-pauth.c: New test.
	* gdb.arch/aarch64-pauth.exp: New file.