bug#19868: #19868 25.0.50; Compilation eats buffers

[Noam Postavsky <npostavs@users.sourceforge.net>]

retitle 19868 [w32] restarting compilation hangs trying to kill process
found 19868 25.1
quit

> I tried this on Windows 7 and XP, and both show the same correct
> behavior.
>
> It could be that what you see is specific to Windows 8, or to 64-bit
> programs, or to how MinGW64 sets up the process in its startup code (I
> used MinGW32).
>
> You say above that Emacs hangs inside the delete-process call -- can
> you show a backtrace in that state, preferably from an unoptimized
> build?  I'd like to see where exactly it hangs.

I reproduced this (the hanging, not the buffer eating) on Windows 10,
Emacs 25.1, MinGW64.  Stepping with gdb I found the the hang occurs in
sys_close where it calls _close (fd).  This is being called from
deactivate_process:

  for (i = 0; i < PROCESS_OPEN_FDS; i++)
    close_process_fd (&p->open_fd[i]); // <-- when i == 2