Split up the all and opt (native code) rules, and allow the curses
library to be specified explicitly.

diff -ur mingw32-ocaml-curses-20020319.orig/curses/Makefile mingw32-ocaml-curses-20020319.mingw/curses/Makefile
--- mingw32-ocaml-curses-20020319.orig/curses/Makefile	2002-03-19 13:07:47.000000000 +0000
+++ mingw32-ocaml-curses-20020319.mingw/curses/Makefile	2008-11-15 23:03:35.000000000 +0000
@@ -5,15 +5,17 @@
 LFLAGS=
 CPP=cpp
 
-CURSES=ncurses
+CURSES=-lncurses
 
-all: libmlcurses.a mlcurses.cma mlcurses.cmxa
+all: libmlcurses.a mlcurses.cma
+
+opt: libmlcurses.a mlcurses.cmxa
 
 ml_curses.o: ml_curses.c functions.c
 	$(OCAMLC) -ccopt "$(CFLAGS)" -c $<
 
 libmlcurses.a: ml_curses.o
-	$(OCAMLMKLIB) -o mlcurses $< -l$(CURSES)
+	$(OCAMLMKLIB) -o mlcurses $< $(CURSES)
 
 mlcurses.cma: curses.cmo
 	$(OCAMLMKLIB) -o mlcurses -linkall $^