ColdFire: Update cpu flag for 4.2-xx compiler

Signed-off-by: TsiChungLiew <Tsi-Chung.Liew@freescale.com>
diff --git a/cpu/mcf523x/config.mk b/cpu/mcf523x/config.mk
index ba324a8..93645a3 100644
--- a/cpu/mcf523x/config.mk
+++ b/cpu/mcf523x/config.mk
@@ -24,4 +24,8 @@
 #
 
 PLATFORM_RELFLAGS += -ffixed-d7 -msep-data
+ifeq ($(findstring 4.2,$(shell $(CC) --version)),4.2)
+PLATFORM_CPPFLAGS += -mcpu=5235 -fPIC
+else
 PLATFORM_CPPFLAGS += -m5307 -fPIC
+endif