Sometimes it's faster (and the compiler might be able to optimize
better) to include all source files of a project into one source file
and compile only this one file instead of all files each one by one.
This can be done with the macro CREATE_FINAL_FILE().
This example creates an executable named "foo" from the sources
main.cpp, app.cpp, bar.c and foo.c. If the option "ENABLE_FINAL" is
enabled, these for files will be included in the file "_final.cpp" and
only this will be compiled. Otherwise the four source files are compiled
one by one as you know it. And here comes the macro: