MIPS: Fix MSA toolchain support detection.

The '-mmsa' option is not supported by all current compilers. Change
the detection to instead pass the option directly to the assembler.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Reviewed-by: Paul Burton <Paul.Burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/6835/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Makefile

@@ -120,7 +120,7 @@ cflags-$(CONFIG_SB1XXX_CORELIS)	+= $(call cc-option,-mno-sched-prolog) \
 				   -fno-omit-frame-pointer
 
 ifeq ($(CONFIG_CPU_HAS_MSA),y)
-toolchain-msa			:= $(call cc-option-yn,-mhard-float -mfp64 -mmsa)
+toolchain-msa	:= $(call cc-option-yn,-mhard-float -mfp64 -Wa$(comma)-mmsa)
 cflags-$(toolchain-msa)		+= -DTOOLCHAIN_SUPPORTS_MSA
 endif