While info-build already provides lots of useful information
    it does not print the application source dir. However this
    might be useful for debugging and logging, hence its added
    to the output.

Add a target to print an internal variable value.

Usage: make info-debug-variable-VARIABLENAME

Example:

    make info-debug-variable-ELFFILE
    /path/to/riot/examples/hello-world/bin/native/hello-world.elf

* Use the existing variable when possible
* Remove duplicate definition
* Remove unused BINFILE variable

Add INCLUDES to the output of info-build