makefile: Check for dirty submodules when building

Makefile.common

@@ -6,6 +6,7 @@ DEBUG ?= 1
 # optimization
 OPT ?= -Og
 
+CHECK_DIRTY_SUBMODULE ?= 1
 
 #######################################
 # paths
@@ -242,11 +243,20 @@ Core/Inc/githash.h:
 Core/Src/main.c: Core/Inc/githash.h
 Core/Src/retro-go/rg_main.c: Core/Inc/githash.h
 
-$(BUILD_DIR)/%.o: %.c Makefile.common Makefile $(LDSCRIPT) $(SDK_HEADERS) | $(BUILD_DIR)
+ifeq (${CHECK_DIRTY_SUBMODULE},1)
+CheckDirtySubmodules:
+	$(V)git submodule foreach "git diff --quiet" 2> /dev/null || \
+		(echo -e "\n\n\nYou are using dirty submodules.\nPlease sync the submodules by running 'git submodule update --init'\n\n(You may set CHECK_DIRTY_SUBMODULE=0 to suppress this warning)\n\n\n" && exit 1)
+else
+CheckDirtySubmodules:
+endif
+.PHONY: CheckDirtySubmodules
+
+$(BUILD_DIR)/%.o: %.c Makefile.common Makefile $(LDSCRIPT) $(SDK_HEADERS) | $(BUILD_DIR) CheckDirtySubmodules
 	$(V)$(ECHO) [ CC ] $(notdir $<)
 	$(V)$(CC) -c $(CFLAGS) -Wa,-a,-ad,-alms=$(BUILD_DIR)/$(notdir $(<:.c=.lst)) $< -o $@
 
-$(BUILD_DIR)/%.o: %.s Makefile.common Makefile $(LDSCRIPT) | $(BUILD_DIR)
+$(BUILD_DIR)/%.o: %.s Makefile.common Makefile $(LDSCRIPT) | $(BUILD_DIR) CheckDirtySubmodules
 	$(V)$(ECHO) [ AS ] $(notdir $<)
 	$(V)$(AS) -c $(CFLAGS) $< -o $@