as: MD

 
 2.10 Dependency Tracking: '--MD'
 ================================
 
 'as' can generate a dependency file for the file it creates.  This file
 consists of a single rule suitable for 'make' describing the
 dependencies of the main source file.
 
    The rule is written to the file named in its argument.
 
    This feature is used in the automatic updating of makefiles.