sh: Don't let SH-4A clobber SH-4 CFLAGS.

Older compilers don't support the -m4a{,nofpu} flags, which has the
side-effect of allowing FP operations to be emitted. Switch this to
incremental tuning, so we at least have -m4-nofpu as a fallback for
the gcc3 toolchains.

Without this, certain modules emit references to __udivsi3_i4 and
__sdivsi3_i4.
Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/Makefile

@@ -35,12 +35,12 @@ endif
 endif
 
 cflags-$(CONFIG_CPU_SH2)		:= $(call cc-option,-m2,)
-cflags-$(CONFIG_CPU_SH2A)		:= $(call cc-option,-m2a,) \
+cflags-$(CONFIG_CPU_SH2A)		+= $(call cc-option,-m2a,) \
 					   $(call cc-option,-m2a-nofpu,)
 cflags-$(CONFIG_CPU_SH3)		:= $(call cc-option,-m3,)
 cflags-$(CONFIG_CPU_SH4)		:= $(call cc-option,-m4,) \
 	$(call cc-option,-mno-implicit-fp,-m4-nofpu)
-cflags-$(CONFIG_CPU_SH4A)		:= $(call cc-option,-m4a,) \
+cflags-$(CONFIG_CPU_SH4A)		+= $(call cc-option,-m4a,) \
 					   $(call cc-option,-m4a-nofpu,)
 
 cflags-$(CONFIG_CPU_BIG_ENDIAN)		+= -mb