build: fix arch cflags not being used when compiling C++ files

Makefile

@@ -85,7 +85,7 @@ $(BUILD_DIR)/%.o: %.c
 $(BUILD_DIR)/%.o: %.cpp
 	@printf "    \033[1;32mCXX\033[0m    \033[35m$(KERNEL_EXEC)\033[0m/$<\n"
 	@mkdir -p $(@D)
-	@$(CXX) $< -o $@ -c $(CXXFLAGS) $(ARCH_CXXFLAGS) -MMD $(KERNEL_DEFINES)
+	@$(CXX) $< -o $@ -c $(CXXFLAGS) $(ARCH_CFLAGS) -MMD $(KERNEL_DEFINES)
 
 clean:
 	@printf "    \033[1;93mRM\033[0m     Deleting build files.\n"