Fix WINDOWSNT/DOS_NT build
Recent changes in sysdep.c and emacsclient unnecessarily removed useful code from DOS_NT builds. This changeset reinstates that code. * nt/inc/ms-w32.h (tcdrain): Redirect to _commit. (fdatasync): No need to redirect anymore. * lib-src/emacsclient.c (flush_stdout): Don't avoid calling tcdrain on DOS_NT platforms. * src/sysdep.c (reset_sys_modes): Don't ifdef away the call to tcdrain on DOS_NT platforms.