6 Second make invocation

Because of the INTERNAL_tool_NAME variable being a non-empty string (while it was empty in the previous top-level invocation), tool.make will include the actual rules to build the tool; in particular, the internal-tool-all rule, which is then executed and builds the tool. All variables such as OBJC_FILES or the library flags are now available directly in the makefiles, they have already been prepared and preprocessed, so that the rules in tool.make can just plainly use these variables naively to perform their job (compiling, installing, or whatever).