powerpc: Don't use -mno-strict-align on clang

We added -mno-strict-align in commit f036b368 (powerpc: Work around little
endian gcc bug) to fix gcc bug http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57134

Clang doesn't understand it. We need to use a conditional because we can't use the
simpler call cc-option here.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Makefile

@@ -66,7 +66,10 @@ endif
 UTS_MACHINE := $(OLDARCH)
 
 ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
-override CC	+= -mlittle-endian -mno-strict-align
+override CC	+= -mlittle-endian
+ifneq ($(COMPILER),clang)
+override CC	+= -mno-strict-align
+endif
 override AS	+= -mlittle-endian
 override LD	+= -EL
 override CROSS32CC += -mlittle-endian