merge libffi/src/powerpc

upstream libffi d3d06f4c, fa1040c1, 590663b3
PowerPC64 ELFv1 option override for Go

Otherwise r11 is loaded from the OPD by indirect function calls.

	* config/rs6000/linux64.h (SUBSUBTARGET_OVERRIDE_OPTIONS): Force
	TARGET_POINTERS_TO_NESTED_FUNCTIONS off when compiling Go.