How to call Makefile from another Makefile?

I’m not really too clear what you are asking, but using the -f command line option just specifies a file – it doesn’t tell make to change directories. If you want to do the work in another directory, you need to cd to the directory:

clean:
    cd gtest-1.4.0 && $(MAKE) clean

Note that each line in Makefile runs in a separate shell, so there is no need to change the directory back.