Patch 12 of 14 (https://gcc.gnu.org/ml/gcc-patches/2014-09/msg01475.html) will 
break bigendian targets implementing vec_shr. This is a PowerPC parallel of 
patch 13 of 14 (https://gcc.gnu.org/ml/gcc-patches/2014-09/msg01477.html) for 
AArch64. I've checked I can build a stage 1 compiler for powerpc-none-eabi and 
that the assembly output looks plausible but no further than that.

In fact I find BYTES_BIG_ENDIAN is defined to true on powerpcle-none-eabi as 
well as powerpc-none-eabi (and also on ppc64-none-elf, but to false on 
ppc64le-none-elf), so I'm not quite sure how your backend works in this regard - 
nonetheless I hope this is a helpful starting point even if not definitive.

gcc/ChangeLog:

	* config/rs6000/vector.md (vec_shl_<mode>): Remove.
	(vec_shr_<mode>): Reverse shift if BYTES_BIG_ENDIAN.