Should we scrap -MG?

[Neil Booth <neil at daikokuya dot demon dot co dot uk>]

Does anyone know of any good use of this option, which prints
dependencies on missing header files.

I see at least two problems with this:-

o We don't know if the header file really should exist or not (!?)
o We don't know in which directory it should exist
o We don't know if the absent header includes other headers.

Basically, I see little point in being able to generate dependencies
for something we cannot preprocess, let alone compile, and "handling"
this considerably obfuscates some of cpplib.

This came up in a private discussion with Zack; I then asked Tom Tromey
if he knew of any sane use of it and he couldn't think of one either.

Neil.