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/linux.2020

@@ -164,6 +164,16 @@ WINOBJ = $(sort $(WINOBJ0))
 # prevent duplicates in VARDATND if both X11 and Qt are being supported
 VARDATND += $(sort $(VARDATND0))
 
+ifdef WANT_LIBNH
+CFLAGS += -DSHIM_GRAPHICS -DNOTTYGRAPHICS -DNOSHELL -DLIBNH
+WINOBJ = winshim.o
+MOREALL += ( cd src ; $(MAKE) pregame ; $(MAKE) libnethack.a )
+libnethack.a: $(HOBJ) $(SYSOBJ) $(WINOBJ) ../lib/lua/liblua.a
+	$(AR) rcs $@ $(HOBJ) $(WINOBJ) ../lib/lua/liblua.a
+	@echo "$@ built."
+winshim.o : ../win/shim/winshim.c $(HACK_H)
+	$(CC) $(CFLAGS) -c -o$@ $<
+endif  # BUILD_LIBNH
 
 #PREFIX=/usr
 PREFIX=$(wildcard ~)/nh/install