[MIPS] Use -Werror on TX39/TX49 boards

Now these directories can be built cleanly.
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/tx4927/common/Makefile

@@ -10,3 +10,5 @@ obj-y	+= tx4927_prom.o tx4927_setup.o tx4927_irq.o
 
 obj-$(CONFIG_TOSHIBA_FPCIB0)	   += smsc_fdc37m81x.o
 obj-$(CONFIG_KGDB)                 += tx4927_dbgio.o
+
+EXTRA_CFLAGS += -Werror

arch/mips/tx4927/toshiba_rbtx4927/Makefile

 obj-y	+= toshiba_rbtx4927_prom.o
 obj-y	+= toshiba_rbtx4927_setup.o
 obj-y	+= toshiba_rbtx4927_irq.o
+
+EXTRA_CFLAGS += -Werror

arch/mips/tx4938/common/Makefile

@@ -9,3 +9,4 @@
 obj-y	+= prom.o setup.o irq.o
 obj-$(CONFIG_KGDB) += dbgio.o
 
+EXTRA_CFLAGS += -Werror

arch/mips/tx4938/toshiba_rbtx4938/Makefile

@@ -7,3 +7,5 @@
 #
 
 obj-y	+= prom.o setup.o irq.o spi_eeprom.o
+
+EXTRA_CFLAGS += -Werror