[Darwin, PPC, testsuite] Exclude darwin from VSX, power8 and power9.

[Darwin, PPC, testsuite] Exclude darwin from VSX, power8 and power9.

If we build Darwin with a modern assembler, then it might well
recognise insns that cannot be used on current Darwin systems.

The patch augments the tests for feature support for VSX,
power8 and power9 to exclude Darwin even if the assembler can
handle the instructions.

gcc/testsuite/

2019-11-01  Iain Sandoe  <iain@sandoe.co.uk>

	Backport from mainline.
	2019-05-15  Iain Sandoe  <iain@sandoe.co.uk>

	* lib/target-supports.exp
	(check_effective_target_powerpc_p8vector_ok): No support for Darwin.
	(check_effective_target_powerpc_p9vector_ok): Likewise.
	(check_effective_target_powerpc_float128_sw_ok): Likewise.
	(check_effective_target_powerpc_float128_hw_ok): Likewise.
	(check_effective_target_powerpc_vsx_ok): Likewise.
	* gcc.target/powerpc/bfp/bfp.exp: Don't try to run this for Darwin.
	* gcc.target/powerpc/dfp/dfp.exp: Likewise.

From-SVN: r277716