* configure.tgt (i[34567]86-*-mingw32*): Set gdb_target = mingw.
* win32-nat.c: Only include cygwin.h on Cygwin host. Don't
include procfs.h.
(cygwin_load_start, cygwin_load_end, cygwin_exceptions): Disable
if not building on Cygwin.
(win32_make_so, handle_output_debug_string, handle_exception)
(do_initial_win32_stuff): Wrap Cygwin specific code in __CYGWIN__.
(win32_attach): Only fallback to Cygwin pids if building on
Cygwin.
(win32_pid_to_exec_file): Disable Cygwin specific code, if not
building on Cygwin.
(win32_create_inferior): Disable starting the inferior through a
shell, environment var processing and tty handling if not building
on Cygwin.
(cygwin_pid_to_str): Rename to ...
(win32_pid_to_str): ... this.
(init_win32_ops): Update use of win32_pid_to_str. Disable "shell"
and "cygwin-exceptions" commands if not building on Cygwin.
