This option instructs the compiler to compile the source and write makefile dependency lines to a file.
The output file is suitable for use by a make utility.
The compiler names the file
the name of the source file. If you specify multiple source files,
a dependency file is created for each source file.
If you want to produce makefile dependencies and preprocessor
source file output in a single step, you can do so using the combination
--md -P to suppress line number generation).