fixed color detection routine in makefile

tmk_core/rules.mk

@@ -161,10 +161,8 @@ CFLAGS += -fshort-enums
 CFLAGS += -fno-strict-aliasing
 # add color
 ifeq ($(COLOR),true)
-ifeq ("$(shell echo "int main(){}" | $(CC) -fdiagnostics-color -x c - -o /dev/null 2>&1)", "")
+ifeq ("$(echo "int main(){}" | $(CC) -fdiagnostics-color -x c - -o /dev/null 2>&1)", "")
 	CFLAGS+= -fdiagnostics-color
-else ifeq ("$(shell echo "int main(){}" | $(CC) -fcolor-diagnostics -x c - -o /dev/null 2>&1)", "")
-	CFLAGS+= -fcolor-diagnostics
 endif
 endif
 CFLAGS += -Wall