Fix name of makefile dep files

The files can't start with a .dot, as the wildcard function wont
find them. So this is fixed by removing the BUILD_DIR from the
name.

tmk_core/rules.mk

@@ -260,7 +260,7 @@ LST = $(patsubst %.c,$(OBJDIR)/%.lst,$(patsubst %.cpp,$(OBJDIR)/%.lst,$(patsubst
 
 # Compiler flags to generate dependency files.
 #GENDEPFLAGS = -MMD -MP -MF .dep/$(@F).d
-GENDEPFLAGS = -MMD -MP -MF $(BUILD_DIR)/.dep/$(subst /,_,$@).d
+GENDEPFLAGS = -MMD -MP -MF $(BUILD_DIR)/.dep/$(subst /,_,$(subst $(BUILD_DIR)/,,$@)).d
 
 
 # Combine all necessary flags and optional flags.