[PATCH] uml: fix compile failure for TT mode

Without this patch, uml compile fails with:

  LD      .tmp_vmlinux1
arch/um/kernel/built-in.o: In function `config_gdb_cb':
arch/um/kernel/tt/gdb.c:129: undefined reference to `TASK_EXTERN_PID'

Tested on i386, but fix needed on x86_64 too AFAICS.

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>