makefiles: make it easier to use ccache for build on windows

makefiles/toolchain_gnu-arm-eabi.mk

@@ -228,7 +228,7 @@ DEP_INCLUDES		 = $(subst .o,.d,$(OBJS))
 define COMPILE
 	@$(ECHO) "CC:      $1"
 	@$(MKDIR) -p $(dir $2)
-	$(Q) $(CC) -MD -c $(CFLAGS) $(abspath $1) -o $2
+	$(Q) $(CCACHE) $(CC) -MD -c $(CFLAGS) $(abspath $1) -o $2
 endef
 
 # Compile C++ source $1 to $2
@@ -237,7 +237,7 @@ endef
 define COMPILEXX
 	@$(ECHO) "CXX:     $1"
 	@$(MKDIR) -p $(dir $2)
-	$(Q) $(CXX) -MD -c $(CXXFLAGS) $(abspath $1) -o $2
+	$(Q) $(CCACHE) $(CXX) -MD -c $(CXXFLAGS) $(abspath $1) -o $2
 endef
 
 # Assemble $1 into $2