Better "include guards" for the makefiles

Checking for ARCH is not good enough, since some subprojects define it.
Ergodox Ez for example. The leads to running the make from
keyboards/ergodox/ez failing. The keyboard makefile will not be included
in that case, and therefore not the CUSTOM_MATRIX either.

Furthermore the output files are read from many different .build
directories, so it doesn't fail deterministically. For example on the
Travis CI the compilation passes, since there's no outdated objects that
needs recompilation.

Makefile

@@ -5,8 +5,9 @@ endif
 .DEFAULT_GOAL := all
 
 space := $(subst ,, )
-starting_makefile := $(subst $(space),_SPACE_,$(abspath $(firstword $(MAKEFILE_LIST))))
-mkfile_path := $(subst $(space),_SPACE_,$(abspath $(lastword $(MAKEFILE_LIST))))
+ESCAPED_ABS_PATH = $(subst $(space),_SPACE_,$(abspath $1))
+starting_makefile := $(call ESCAPED_ABS_PATH,$(firstword $(MAKEFILE_LIST)))
+mkfile_path := $(call ESCAPED_ABS_PATH,$(lastword $(MAKEFILE_LIST))))
 abs_tmk_root := $(patsubst %/,%,$(dir $(mkfile_path)))
 
 ifneq (,$(findstring /keyboards/,$(starting_makefile)))
@@ -83,10 +84,8 @@ endif
 
 ifneq ("$(wildcard $(KEYBOARD_PATH)/$(KEYBOARD).c)","")
 	KEYBOARD_FILE = keyboards/$(KEYBOARD)/$(KEYBOARD).c
-	ifndef ARCH
-		ifneq ("$(wildcard $(KEYBOARD_PATH)/Makefile)","")
-			include $(KEYBOARD_PATH)/Makefile
-		endif
+	ifneq ($(call ESCAPED_ABS_PATH,$(KEYBOARD_PATH)/Makefile),$(starting_makefile))
+		-include $(KEYBOARD_PATH)/Makefile
 	endif
 else 
 $(error "$(KEYBOARD_PATH)/$(KEYBOARD).c" does not exist)
@@ -101,7 +100,9 @@ ifdef SUBPROJECT
 	ifneq ("$(wildcard $(SUBPROJECT_PATH)/$(SUBPROJECT).c)","")
 		OPT_DEFS += -DSUBPROJECT_$(SUBPROJECT)
 		SUBPROJECT_FILE = keyboards/$(KEYBOARD)/$(SUBPROJECT)/$(SUBPROJECT).c
+		ifneq ($(call ESCAPED_ABS_PATH,$(SUBPROJECT_PATH)/Makefile),$(starting_makefile))
 			-include $(SUBPROJECT_PATH)/Makefile
+		endif
 	else 
 $(error "$(SUBPROJECT_PATH)/$(SUBPROJECT).c" does not exist)
 	endif
@@ -119,15 +120,19 @@ endif
 KEYMAP_PATH = $(KEYBOARD_PATH)/keymaps/$(KEYMAP)
 ifneq ("$(wildcard $(KEYMAP_PATH)/keymap.c)","")
 	KEYMAP_FILE = keyboards/$(KEYBOARD)/keymaps/$(KEYMAP)/keymap.c
+	ifneq ($(call ESCAPED_ABS_PATH,$(KEYMAP_PATH)/Makefile),$(starting_makefile))
 		-include $(KEYMAP_PATH)/Makefile
+	endif
 else 
 	ifeq ("$(wildcard $(SUBPROJECT_PATH)/keymaps/$(KEYMAP)/keymap.c)","")
 $(error "$(KEYMAP_PATH)/keymap.c" does not exist)
 	else
 		KEYMAP_PATH = $(SUBPROJECT_PATH)/keymaps/$(KEYMAP)
 		KEYMAP_FILE = keyboards/$(KEYBOARD)/$(SUBPROJECT)/keymaps/$(KEYMAP)/keymap.c
+		ifneq ($(call ESCAPED_ABS_PATH,$(KEYMAP_PATH)/Makefile),$(starting_makefile))
 			-include $(KEYMAP_PATH)/Makefile
 		endif
+	endif
 endif
 
 ifdef SUBPROJECT