build system: and gcc8 warnings compatibility option

Kconfig

@@ -176,6 +176,13 @@ config WARN_WRITE_STRINGS
         For C++, this warns about the deprecated conversion from string
         literals to ``char *``.
 
+config DISABLE_GCC8_WARNINGS
+    bool "Disable new warnings introduced in GCC 6 - 8"
+    default "n"
+    help
+        Enable this option if using GCC 6 or newer, and wanting to disable warnings which don't appear with GCC 5.
+
+
 endmenu # Compiler Options
 
 menu "Component config"

make/project.mk

@@ -273,10 +273,28 @@ COMMON_WARNING_FLAGS = -Wall -Werror=all \
 	-Wno-error=unused-function \
 	-Wno-error=unused-but-set-variable \
 	-Wno-error=unused-variable \
+	-Wno-error=unused-const-variable \
 	-Wno-error=deprecated-declarations \
 	-Wextra \
 	-Wno-unused-parameter -Wno-sign-compare
 
+ifdef CONFIG_DISABLE_GCC8_WARNINGS
+COMMON_WARNING_FLAGS += -Wno-parentheses \
+	-Wno-sizeof-pointer-memaccess \
+	-Wno-clobbered \
+	-Wno-format-overflow \
+	-Wno-stringop-truncation \
+	-Wno-misleading-indentation \
+	-Wno-cast-function-type \
+	-Wno-implicit-fallthrough \
+	-Wno-unused-const-variable \
+	-Wno-switch-unreachable \
+	-Wno-format-truncation \
+	-Wno-memset-elt-size \
+	-Wno-int-in-bool-context
+endif
+
+
 ifdef CONFIG_WARN_WRITE_STRINGS
 COMMON_WARNING_FLAGS += -Wwrite-strings
 endif #CONFIG_WARN_WRITE_STRINGS