Move scoped_ignore_sigttou to gdbsupport/

Move scoped_ignore_sigttou to gdbsupport/

A following patch will want to use scoped_ignore_sigttou in code
shared between GDB and GDBserver.  Move it under gdbsupport/.

Note that despite what inflow.h/inflow.c's first line says, inflow.c
is no longer about ptrace, it is about terminal management.  Some
other files were unnecessarily including inflow.h, I guess a leftover
from the days when inflow.c really was about ptrace.  Those inclusions
are simply dropped.

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <pedro@palves.net>

	* Makefile.in (HFILES_NO_SRCDIR): Remove inflow.h.
	* inf-ptrace.c, inflow.c, procfs.c: Don't include "inflow.h".
	* inflow.h: Delete, moved to gdbsupport/ under a different name.
	* ser-unix.c: Don't include "inflow.h".  Include
	"gdbsupport/scoped_ignore_sigttou.h".

gdbsupport/ChangeLog:
yyyy-mm-dd  Pedro Alves  <pedro@palves.net>

	* scoped_ignore_sigttou.h: New file, moved from gdb/ and renamed.

Change-Id: Ie390abf42c3a78bec6d282ad2a63edd3e623559a