PowerPC: Add future hwcap2 bits

PowerPC: Add future hwcap2 bits

This patch adds support for the two new HWCAP2 fields used by the
__builtin_cpu_supports function.  It adds support in the target_clones
attribute for -mcpu=future.

The two new __builtin_cpu_supports tests are:
	__builtin_cpu_supports ("isa_3_1")
	__builtin_cpu_supports ("mma")

The bits used are the bits that the Linux kernel engineers will be using for
these new features.

gcc/
2020-06-09  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/ppc-auxv.h (PPC_PLATFORM_FUTURE): Allocate
	'future' PowerPC platform.
	(PPC_FEATURE2_ARCH_3_1): New HWCAP2 bit for ISA 3.1.
	(PPC_FEATURE2_MMA): New HWCAP2 bit for MMA.
	* config/rs6000/rs6000-call.c (cpu_supports_info): Add ISA 3.1 and
	MMA HWCAP2 bits.
	* config/rs6000/rs6000.c (CLONE_ISA_3_1): New clone support.
	(rs6000_clone_map): Add 'future' system target_clones support.

testsuite/
2020-06-09  Michael Meissner  <meissner@linux.ibm.com>

	* gcc.target/powerpc/clone3.c: New test for using 'future' with
	the target_clones attribute.