* pexecute.c (pexecute): New function for mingw32. Supports pipes.
        (pwait): New function for mingw32.
        * gcc.c (execute): Mingw32 pexecute() supports pipes, but cygwin32
        pipe support is broken for now.

Co-Authored-By: J.J. VanderHeijden <J.J.vanderHeijden@student.utwente.nl>

From-SVN: r17396