Introduce project-specific dosbox.conf

With the stock configuration, DOSBox limits the amount of instructions
it emulates each millisecond to a value it guesses. This is a reasonable
default to have when emulating games or other software from the time,
but woefully slow for our purposes of compilation.

Since the user's configuration file will most likely be tailored to
other uses, it makes sense, then, to use a project-specific
configuration here and override any user configuration. For now, set
only the cycles setting to 'max'.

The DOSBox invocation in the Makefile gets a bit long with the addition
of the -conf flag, so contain it in a variable instead.

Makefile

@@ -1,3 +1,5 @@
+DOSBOX=dosbox -conf dosbox.conf -exit
+
 ordos.img: BOOT.BIN IO.SYS ORDOS.SYS COMMAND.COM debug.com edlin.com exe2bin.exe link.exe masm.exe
 	rm -f ordos.img
 	mkfs.fat -C $@ -M 0xff 320
@@ -12,16 +14,16 @@ ordos.img: BOOT.BIN IO.SYS ORDOS.SYS COMMAND.COM debug.com edlin.com exe2bin.exe
 	mcopy -i $@ masm.exe ::
 
 BOOT.BIN: boot.asm
-	dosbox -exit mk-boot.bat
+	$(DOSBOX) mk-boot.bat
 
 IO.SYS: io.asm
-	dosbox -exit mk-io.bat
+	$(DOSBOX) mk-io.bat
 
 ORDOS.SYS: msdos.asm stddos.asm
-	dosbox -exit mk-ordos.bat
+	$(DOSBOX) mk-ordos.bat
 
 COMMAND.COM: command.asm
-	dosbox -exit mk-comma.bat
+	$(DOSBOX) mk-comma.bat
 
 clean:
 	rm -f ordos.img *.OBJ *.EXE *.COM *.BIN *.SYS

dosbox.conf

@@ -0,0 +1,2 @@
+[cpu]
+cycles=max