Automatic compilation of correct version

luprex/Makefile

@@ -1,25 +1,18 @@
 
-ifeq ($(OS),mingw)
-  EXE=main.exe
-  LIBS=-L./ext/openssl-mingw -lssl -lcrypto -lws2_32 -lcrypt32 -lcryptui
-  LUAFLAGS=-DLUA_USE_APICHECK -DLUA_COMPAT_ALL
-  OPT=-g -O0
-  DRIVER=driver-mingw
-else ifeq ($(OS),linux)
+ifneq "" "$(findstring -linux-,$(MAKE_HOST))"
   EXE=main
   LIBS=-L./ext/openssl-linux -lssl -lcrypto
   LUAFLAGS=-DLUA_USE_APICHECK -DLUA_USE_POSIX
   OPT=-g -O0
   DRIVER=driver-linux
+else ifneq "" "$(findstring cmd.exe,$(COMSPEC))"
+  EXE=main.exe
+  LIBS=-L./ext/openssl-mingw -lssl -lcrypto -lws2_32 -lcrypt32 -lcryptui
+  LUAFLAGS=-DLUA_USE_APICHECK -DLUA_COMPAT_ALL
+  OPT=-g -O0
+  DRIVER=driver-mingw
 else
-  # In this case, any attempt to build luprex will trigger an error,
-  # But making 'clean' will still work.
-  ERROR=$(error You must specify OS=linux or OS=mingw)
-  EXE=$(ERROR)
-  LIBS=$(ERROR)
-  LUAFLAGS=$(ERROR)
-  OPT=$(ERROR)
-  DRIVER=driver-xxx
+  $(error Cannot figure out whether to build the linux or mingw version)
 endif