[gtkmm] GLIBMM dispatcher comment

["Andrew E. Makeev" <andrew solvo ru>]

If you will just set this function in dispatcher.cc as:

/* Try to set the close-on-exec flag of the file descriptor,
 * so that it won't be leaked if a new process is spawned.
 */
void fd_set_close_on_exec(int fd)
{
#ifndef G_OS_WIN32
  const int flags = fcntl(fd, F_GETFD, 0);
  g_return_if_fail(flags >= 0);

  fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
#endif
}

you will get dispatcher working on WIN32 platform.

Such behavior is possible because WIN32 removes pipes automatically when
program exits.

For now it looks like dispatcher is not used at all when building
sources on WIN32.

Regards,
-andrew