Add tweaks for Cygwin support

[SineSwiper]

The Cygwin team has their own patch for the source, but it should be ported into master, so that it can be built from source unaltered:

From http://cygwin.mirror.constant.com/x86_64/release/lua-lfs/lua-lfs-1.6.2-2-src.tar.xz

--- origsrc/luafilesystem-1.6.2/Makefile        2012-10-04 09:25:54.000000000 -0500
+++ src/luafilesystem-1.6.2/Makefile    2013-11-10 15:49:27.428034500 -0600
@@ -12,7 +12,7 @@ OBJS= src/$T.o
 lib: src/lfs.so

 src/lfs.so: $(OBJS)
-       MACOSX_DEPLOYMENT_TARGET="10.3"; export MACOSX_DEPLOYMENT_TARGET; $(CC) $(CFLAGS) $(LIB_OPTION) -o src/lfs.so $(OBJS)
+       MACOSX_DEPLOYMENT_TARGET="10.3"; export MACOSX_DEPLOYMENT_TARGET; $(CC) $(CFLAGS) $(LIB_OPTION) -o src/lfs.so $(OBJS) -llua

 install:
        mkdir -p $(LUA_LIBDIR)
--- origsrc/luafilesystem-1.6.2/src/lfs.c       2012-10-04 09:25:54.000000000 -0500
+++ src/luafilesystem-1.6.2/src/lfs.c   2013-11-10 15:51:04.909610100 -0600
@@ -54,6 +54,9 @@
 #include <fcntl.h>
 #include <sys/types.h>
 #include <utime.h>
+#ifdef __CYGWIN__
+#include <io.h>
+#endif
 #endif

 #include <lua.h>
@@ -114,9 +117,15 @@ typedef struct dir_data {
 #define STAT_FUNC _stati64
 #define LSTAT_FUNC STAT_FUNC
 #else
+#ifdef __CYGWIN__
+#define _O_TEXT        O_TEXT
+#define _O_BINARY      O_BINARY
+#define lfs_setmode(L,file,m)   ((void)L, _setmode(fileno(file), m))
+#else
 #define _O_TEXT               0
 #define _O_BINARY             0
 #define lfs_setmode(L,file,m)   ((void)L, (void)file, (void)m, 0)
+#endif
 #define STAT_STRUCT struct stat
 #define STAT_FUNC stat
 #define LSTAT_FUNC lstat

The includes look fine as-is, but the Makefile adjustment probably needs a Cygwin if block.