staging: rtl8723au: Add compiler check for -Wtype-limits

Gcc versions before 4.3 do not support -Wtype-limits:

cc1: error: unrecognized command line option "-Wtype-limits"
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723au/Makefile

@@ -52,4 +52,5 @@ r8723au-$(CONFIG_8723AU_AP_MODE) += core/rtw_ap.o
 
 obj-$(CONFIG_R8723AU)	:= r8723au.o
 
-ccflags-y += -Wtype-limits -D__CHECK_ENDIAN__ -I$(src)/include
+ccflags-y += $(call cc-option,-Wtype-limits,)
+ccflags-y += -D__CHECK_ENDIAN__ -I$(src)/include