makefiles/cflags.inc.mk: Use a template for CFLAGS testing

makefiles/cflags.inc.mk

@@ -25,21 +25,23 @@ ifeq ($(shell $(CC) -fno-delete-null-pointer-checks -E - 2>/dev/null >/dev/null
   endif
 endif
 
+# Template for testing a compiler flag and adding it to CFLAGS (errors usually
+# happens when using older toolchains which do not support the given flags)
+define cflags_test_and_add
+  ifeq ($(shell $(CC) $(1) -E - 2>/dev/null >/dev/null </dev/null ; echo $$?),0)
+    CFLAGS += $(1)
+  endif
+endef
 # Use colored compiler output if the compiler supports this and if this is not
 # disabled by the user
 ifeq ($(CC_NOCOLOR),0)
-  ifeq ($(shell $(CC) -fdiagnostics-color -E - 2>/dev/null >/dev/null </dev/null ; echo $$?),0)
-    CFLAGS += -fdiagnostics-color
-  endif
+  $(eval $(call cflags_test_and_add,-fdiagnostics-color))
 endif
 
 # Fast-out on old style function definitions.
 # They cause unreadable error compiler errors on missing semicolons.
 # Worse yet they hide errors by accepting wildcard argument types.
-ifeq ($(shell $(CC) -Wstrict-prototypes -Werror=strict-prototypes -Wold-style-definition -Werror=old-style-definition -E - 2>/dev/null >/dev/null </dev/null ; echo $$?),0)
-  # duplicated parameters don't hurt
-  CFLAGS += -Wstrict-prototypes -Wold-style-definition
-endif
+$(foreach flag,-Wstrict-prototypes -Wold-style-definition,$(eval $(call cflags_test_and_add,$(flag))))
 
 # Unwanted flags for c++
 CXXUWFLAGS += -std=%