libnethack pr385

roll parts of pr385 into source tree

This does not take the PR as is.

Unlike the PR, this streamlines and minimizes the integration somewhat:

- use hints/include mechanism instead of creating alternative
  Makefile.dat, Makefile.src, Makefile.top, Makefile.utl in sys/lib;
  those would have been a maintenance nightmare.

- don't have alternative mkmkfile.sh and setup.sh in sys/lib.

- sys/lib/libnethackmain.c differed from sys/unix/unixmain.c by
  very little, so just place a small bit of conditional code at the
  top of sys/unix/unixmain.c instead.

- changed the conditional code bits from __EMSCRIPTEN__ to
  CROSS_TO_WASM.

- You should be able to build the wasm result by:
    cd sys/unix ; sh setup.sh hints/linux.2020 ; cd ../..
    make fetch-lua    (<-one time)
    make WANT_LIBNH all

- You should be able to build LIBNBH by:
    cd sys/unix ; sh setup.sh hints/linux.2020 ; cd ../..
    make fetch-lua    (<-one time)
    make CROSS_TO_WASM=1 all

As it is currently coded, winshim.c requires C99.

sys/unix/hints/include/multiw-2.2020

@@ -47,6 +47,10 @@ endif
 endif
 endif
 
+ifdef WANT_LIBNH
+WANT_DEFAULT=shim
+endif
+
 # Make sure that a default interface is specified; this doesn't guarantee
 # sanity for something like 'make WANT_WIN_CURSES=1 WANT_DEFAULT=X11' but
 # 'makedefs -v' would notice, complain, and quit causing 'make' to quit.