re PR go/66870 (split stack issues on ppc64le and ppc64)

re PR go/66870 (split stack issues on ppc64le and ppc64)

	PR target/66870
	* config/rs6000/sysv4.h (TARGET_CAN_SPLIT_STACK_64BIT): Define.
	* configure.ac: Define HAVE_GOLD_ALTERNATE_SPLIT_STACK on Power
	based on gold linker version.
	* gcc.c: Add -fuse-ld=gold to STACK_SPLIT_SPEC if
	HAVE_GOLD_ALTERNATE_SPLIT_STACK defined.
	* configure, config.in: Regenerate.
go:
	* gospec.c (lang_specific_driver): Set appropriate split stack
	options for 64 bit compiles based on TARGET_CAN_SPLIT_STACK_64BIT.

From-SVN: r228311