gdb --multi mode stdout redirecting to stderr

gdb --multi mode stdout redirecting to stderr

When in stdio mode (talking to gdb through stdin/stdout, not
through a socket), redirect stdout to stderr and close stdin
for the inferior. That way at least some output can be seen,
but there will be no input.

This is workaround till we have real terminal handling.

     * coregrind/vgdb.c (main): Pass in_port to do_multi_mode.
     (do_multi_mode): Pass in_port to fork_and_exec_valgrind.
     (fork_and_exec_valgrind): Close stdin, redirect stdout to
     stderr if in_port <= 0.

https://bugs.kde.org/show_bug.cgi?id=471311