CEDET calls cpp -E -dM -x c++ /dev/null

[Lennart Borgman]

CEDET does the call above in semantic-gcc-setup. Doing that from the
command line using MingGW on w32 fails.

It fails because /dev/null is not valid on w32. Shouldn't it be NUL
there? However looking through Emacs lisp sources I see several uses
of just /dev/null. Wouldn't it be better to use some defsubst for
this?

Now, if the command instead is

    cpp -E -dM -x c++ nul

it fails for me with

  cpp: installation problem, cannot exec `cc1plus': No such file or directory

Does it work for anyone else using MinGW? What should perhaps be used instead?