add an optional deploy-to-dosbox target for msdos cross-compile

The WANT_DEBUG=1 will cause the cross-compile to include line
number information in the NetHack executable, useful for
backtraces and gdb debugging sessions.

How a developer can use the optional deploy-to-dosbox target:
    make CROSS_TO_MSDOS=1 WANT_DEBUG=1 dosbox=/mnt/c/dosbox deploy-to-dosbox

where dosbox= points to the directory which will be mounted for
your drive in dosbox

THe deploy-to-dosbox recipe ensures that a target copy of gdb.exe
ends up alongside nethack.exe at the target, including:
  - placing the source code that gdb requires on the target
    in the nhsrc subfolder.
  - an nhgdb.bat that supplies the right switches to gdb
    for locating the NetHack sources.

sys/unix/hints/include/cross-post.370

@@ -79,6 +79,65 @@ $(LUABIN):
 dodata:
 	( cd .. && make dlb && cd src)
 
+ifdef dosbox
+# make CROSS_TO_MSDOS=1 dosbox=~/dosbox deploy-to-dosbox
+ifdef MAKEFILE_TOP
+deploy-to-dosbox:
+	( cd src; make $(DEPLOY); cd .. )
+endif
+.PHONY: deploytodosbox
+
+deploytodosbox: ../targets/msdos/NH370DOS.ZIP $(dosboxnhfolder) $(dosboxnhsrc) \
+			$(dosboxnhsrc)/src $(dosboxnhsrc)/include \
+			$(dosboxnhsrc)/sys/msdos $(dosboxnhsrc)/sys/share \
+			$(dosboxnhsrc)/win/share $(dosboxnhsrc)/win/curses \
+			$(dosboxnhsrc)/win/tty $(dosboxnhsrc)/util \
+			$(dosboxnhfolder)/NETHACK.EXE \
+			$(dosboxnhfolder)/GDB.EXE $(dosboxnhfolder)/nhgdb.bat
+	@echo DOS NetHack deployed to dosbox at $(dosboxnhfolder)
+
+$(dosboxnhfolder):
+	mkdir -p $@
+$(dosboxnhsrc): $(dosboxnhfolder)
+	mkdir -p $@
+$(dosboxnhsrc)/src: $(dosboxnhsrc)
+	mkdir -p $@
+	cp --preserve=timestamps $(FLDR)src/*.c $(dosboxnhsrc)/src
+$(dosboxnhsrc)/include: $(dosboxnhsrc)
+	mkdir -p $@
+	cp --preserve=timestamps $(FLDR)include/*.h $(dosboxnhsrc)/include
+$(dosboxnhsrc)/sys/msdos: $(dosboxnhsrc)
+	mkdir -p $@
+	cp --preserve=timestamps $(FLDR)sys/msdos/*.c $(dosboxnhsrc)/sys/msdos
+	cp --preserve=timestamps $(FLDR)sys/msdos/*.h $(dosboxnhsrc)/sys/msdos
+$(dosboxnhsrc)/sys/share: $(dosboxnhsrc)
+	mkdir -p $@
+	cp --preserve=timestamps $(FLDR)sys/share/*.c $(dosboxnhsrc)/sys/share
+$(dosboxnhsrc)/win/share: $(dosboxnhsrc)
+	mkdir -p $@
+	cp --preserve=timestamps $(FLDR)win/share/*.c $(dosboxnhsrc)/win/share
+$(dosboxnhsrc)/win/curses: $(dosboxnhsrc)
+	mkdir -p $@
+	cp --preserve=timestamps $(FLDR)win/curses/*.c $(dosboxnhsrc)/win/curses
+	cp --preserve=timestamps $(FLDR)win/curses/*.h $(dosboxnhsrc)/win/curses
+$(dosboxnhsrc)/win/tty: $(dosboxnhsrc)
+	mkdir -p $@
+	cp --preserve=timestamps $(FLDR)win/tty/*.c $(dosboxnhsrc)/win/tty
+$(dosboxnhsrc)/util: $(dosboxnhsrc)
+	mkdir -p $@
+	cp --preserve=timestamps $(FLDR)util/*.c $(dosboxnhsrc)/util
+	cp --preserve=timestamps $(FLDR)util/*.h $(dosboxnhsrc)/util
+$(dosboxnhfolder)/NETHACK.EXE: $(TARGETPFX)NH370DOS.ZIP
+	unzip -o $(TARGETPFX)NH370DOS.ZIP -d $(dosboxnhfolder)
+	find $(dosboxnhfolder) -type f -name "$(dosboxconfigfile)" \
+		| xargs sed -i 's/#OPTIONS=video:autodetect/OPTIONS=video:autodetect/g'
+$(dosboxnhfolder)/GDB.EXE: $(dosboxnhfolder)
+	curl --output gdb801b.zip $(dosgdburl)
+	unzip -p gdb801b.zip bin/gdb.exe >$@
+	rm gdb801b.zip
+$(dosboxnhfolder)/nhgdb.bat: $(FLDR)src/Makefile
+	echo "gdb -ex 'directory nhsrc/src nhsrc/include nhsrc/sys/msdos nhsrc/sys/share nhsrc/win/share nhsrc/win/curses nhsrc/win/tty nhsrc/util' NETHACK.EXE"> $@
+endif  # dosbox
 endif  # CROSS_TO_MSDOS
 
 ifdef CROSS_TO_WASM

sys/unix/hints/include/cross-pre2.370

@@ -134,6 +134,26 @@ override TARGET_CXX = $(TOOLTOP1)/i586-pc-msdosdjgpp-g++
 override TARGET_AR = $(TOOLTOP1)/i586-pc-msdosdjgpp-gcc-ar
 override TARGET_STUBEDIT = ../lib/djgpp/i586-pc-msdosdjgpp/bin/stubedit
 #
+ifdef DOSBOX
+dosbox=$(DOSBOX)
+endif
+ifdef dosbox
+dosboxgameid=NH370
+dosboxtop=$(dosbox)
+dosboxnhfolder=$(dosboxtop)/$(dosboxgameid)
+dosboxnhsrc=$(dosboxnhfolder)/NHSRC
+dosboxconfigfile=NETHACK.CNF
+dosgdburl=http://www.mirrorservice.org/sites/ftp.delorie.com/pub/djgpp/current/v2gnu/gdb801b.zip
+ifdef MAKEFILE_SRC
+FLDR=../
+endif
+ifdef MAKEFILE_TOP
+FLDR=
+endif
+WANT_DEBUG=1
+DEPLOY=deploytodosbox
+endif  # dosbox
+#
 ifeq "$(WANT_DEBUG)" "1"
 DBGFLAGS = -g
 else