Use macros IS_ANY_SEP, IS_DIRECTORY_SEP,

Use macros IS_ANY_SEP, IS_DIRECTORY_SEP,
IS_DEVICE_SEP, DIRECTORY_SEP, and DEVICE_SEP.
[WINDOWSNT]: Add includes.  Don't define sys_siglist.

(sigchld_handler): Work around bug in MS C compiler.
(sigchld_handler) [WINDOWSNT]: Do not call signal.
(signal_process) [WINDOWSNT]: Use win32_kill_process instead of kill.
(read_process_output) [WINDOWSNT]: Use read_child_output instead of
read.

(create_process) [WINDOWSNT]: Use
pipe_with_inherited_out  and pipe_with_inherited_in.
Use the pid returned by child_setup.  Deal with not having vfork,
Call register_child.
(close_process_descs): Do nothing if WINDOWSNT.

(proc_buffer_char): No longer static.