aarch64: Define __ARM_FEATURE_RCPC

aarch64: Define __ARM_FEATURE_RCPC

https://github.com/ARM-software/acle/pull/199 adds a new feature
macro for RCPC, for use in things like inline assembly.  This patch
adds the associated support to GCC.

Also, RCPC is required for Armv8.3-A and later, but the armv8.3-a
entry didn't include it.  This was probably harmless in practice
since GCC simply ignored the extension until now.  (The GAS
definition is OK.)

gcc/
	* config/aarch64/aarch64.h (AARCH64_FL_FOR_ARCH8_3): Add
	AARCH64_FL_RCPC.
	(AARCH64_ISA_RCPC): New macro.
	* config/aarch64/aarch64-cores.def (thunderx3t110, zeus, neoverse-v1)
	(neoverse-512tvb, saphira): Remove RCPC from these Armv8.3-A+ cores.
	* config/aarch64/aarch64-c.cc (aarch64_update_cpp_builtins): Define
	__ARM_FEATURE_RCPC when appropriate.

gcc/testsuite/
	* gcc.target/aarch64/pragma_cpp_predefs_1.c: Add RCPC tests.