kernel: Add CC_WERROR config to turn warnings into errors

Add configuration option CONFIG_CC_WERROR to prevent warnings
from creeping in.

Signed-off-by: Chris Fries <cfries@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Change-Id: I323b5c3ddee31278da0e6d18b278a2c1327ebd04

Makefile

@@ -398,7 +398,6 @@ KBUILD_CFLAGS   := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
 		   -fno-strict-aliasing -fno-common \
 		   -Werror-implicit-function-declaration \
 		   -Wno-format-security -Wno-builtin-macro-redefined \
-		   -Werror \
 		   -std=gnu89 $(call cc-option,-fno-PIE)
 
 # re-define of __func__, __file__ to save rodata size
@@ -731,6 +730,10 @@ endif
 KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0409, \
 			$(call cc-disable-warning,maybe-uninitialized,))
 
+ifdef CONFIG_CC_WERROR
+KBUILD_CFLAGS	+= -Werror
+endif
+
 # Tell gcc to never replace conditional load with a non-conditional one
 KBUILD_CFLAGS	+= $(call cc-option,--param=allow-store-data-races=0)
 

lib/Kconfig.debug

@@ -1985,6 +1985,16 @@ config TEST_STATIC_KEYS
 
 	  If unsure, say N.
 
+config CC_WERROR
+	bool "Treat all compile warnings as errors"
+	default n
+	help
+	 Select this option to set compiler warnings as errors,
+	 to prevent easily-fixable problems from creeping into
+	 the codebase.
+
+	 If unsure, say N.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"