build: fixed dependency on frame type for px4 build

mk/sketch_sources.mk

@@ -82,6 +82,7 @@ FORCE:
 $(BUILDROOT)/make.flags: FORCE
 	@mkdir -p $(BUILDROOT)
 	@echo "// BUILDROOT=$(BUILDROOT) HAL_BOARD=$(HAL_BOARD) HAL_BOARD_SUBTYPE=$(HAL_BOARD_SUBTYPE) TOOLCHAIN=$(TOOLCHAIN) EXTRAFLAGS=$(EXTRAFLAGS)" > $(BUILDROOT)/make.flags.new
+	@cmp $(BUILDROOT)/make.flags $(BUILDROOT)/make.flags.new > /dev/null 2>&1 || rm -f $(SRCROOT)/*.o
 	@cmp $(BUILDROOT)/make.flags $(BUILDROOT)/make.flags.new > /dev/null 2>&1 || mv $(BUILDROOT)/make.flags.new $(BUILDROOT)/make.flags
 	@rm -f $(BUILDROOT)/make.flags.new
 	@cat $(BUILDROOT)/make.flags