powerpc: Only use -mabi=altivec if toolchain supports it

The -mabi=altivec option is not recognised on LLVM, so use call cc-option
to check for support.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index 7902802..a47e142 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -33,6 +33,6 @@
 obj-$(CONFIG_FTR_FIXUP_SELFTEST) += feature-fixups-test.o
 
 obj-$(CONFIG_ALTIVEC)	+= xor_vmx.o
-CFLAGS_xor_vmx.o += -maltivec -mabi=altivec
+CFLAGS_xor_vmx.o += -maltivec $(call cc-option,-mabi=altivec)
 
 obj-$(CONFIG_PPC64) += $(obj64-y)
diff --git a/lib/raid6/Makefile b/lib/raid6/Makefile
index c7dab06..3b10a48 100644
--- a/lib/raid6/Makefile
+++ b/lib/raid6/Makefile
@@ -15,7 +15,7 @@
                    < $< > $@ || ( rm -f $@ && exit 1 )
 
 ifeq ($(CONFIG_ALTIVEC),y)
-altivec_flags := -maltivec -mabi=altivec
+altivec_flags := -maltivec $(call cc-option,-mabi=altivec)
 endif
 
 # The GCC option -ffreestanding is required in order to compile code containing