kconfig: make kconfig MinGW friendly

kconfig: make kconfig MinGW friendly

Kconfig is powerfull tool. So powerfull that more and more software
projects are using it for configuration. So instead of fixing some of
them one by one, lets fix it in kernel and wait for sync.

This work was originaly done for PTXdist - GPL licensed build system for
userlands and cross-compilers, but it will not hurt kernel kconfig
either. PTXdist menuconfig now works on Windows linked with PDCurses and
compiled using MinGW - there is no termios and signals.

* Do not include <sys/wait.h> and <signal.h> (comes from times when
  lxdialog was separate process)
* Do not mess with termios directly and let curses tell screen size.
  Comment to commit 8d7dc2e6ebe1eb97c3db189290dd69f893775f6d says
  check for screen size could be removed later, but because it didn't
  happen for more than year I left it here as well.
* Save cursor position added by Sam

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Roman Zippel <zippel@linux-m68k.org>