sh: Add -Werror for clean directories.

Follow the MIPS and sparc64 changes for -Werror instrumentation.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
diff --git a/arch/sh/lib/Makefile b/arch/sh/lib/Makefile
index e23dd1a..9dc7b69 100644
--- a/arch/sh/lib/Makefile
+++ b/arch/sh/lib/Makefile
@@ -9,3 +9,5 @@
 memcpy-$(CONFIG_CPU_SH4)	:= memcpy-sh4.o
 
 lib-y	+= $(memcpy-y)
+
+EXTRA_CFLAGS += -Werror