[RFA] Dependency output with -MMD/-MD and -o

[Neil Booth]

Zack Weinberg wrote:-

> Last I looked, -MM excluded files included with <>, but would happily
> stick in /usr/include/stdio.h if it were included with "".  What I
> want is a mode where system headers never get listed and user headers
> always do - using the existing definition of "system headers":
> -isystem directory, or built in.  The idea is that you aren't going to
> be changing /usr/include/stdio.h, and if you do it probably doesn't
> affect the meaning of your program.  But if I include <splay-tree.h>
> from libiberty with <>, I definitely do want it listed in the .d file.

OK, sounds reasonable.

> I don't know off the top of my head how hard this is.  To avoid
> breaking things, it does need a new switch (-MU?)

What does the 'U' mean?

Neil.