-MD together with -save-temps broken

[Neil Booth]

Daniel Egger wrote:-

> -MD still appears to work in cpp (existing behaviour) but is not
> documented in `cpp --help -v`.

Hmm.  I'm not sure what to do about this.  The above command gives

Usage: cpp0 [switches] input output

so it appears that it intends to document the internal interface to
cpp0, which I'd assumed we would leave undocumented.  If this is the
case, then not having -MD and -MMD is correct.

However, if it's meant to document cpp, then we should add -MD and -MMD,
and fix the usage line (to what?  Hardcode "cpp"?)

What do you think, Zack?

Neil.