MSVC: xz: Make file_io.c and file_io.h compatible with MSVC.

Thanks to Kelvin Lee for the original patches
and testing the modifications I made.

src/xz/file_io.c

@@ -39,6 +39,32 @@ static bool warn_fchown;
 
 #include "tuklib_open_stdxxx.h"
 
+#ifdef _MSC_VER
+#	ifdef _WIN64
+		typedef __int64 ssize_t;
+#	else
+		typedef int ssize_t;
+#	endif
+
+	typedef int mode_t;
+#	define S_IRUSR _S_IREAD
+#	define S_IWUSR _S_IWRITE
+
+#	define setmode _setmode
+#	define open _open
+#	define close _close
+#	define lseek _lseeki64
+#	define unlink _unlink
+
+	// The casts are to silence warnings.
+	// The sizes are known to be small enough.
+#	define read(fd, buf, size) _read(fd, buf, (unsigned int)(size))
+#	define write(fd, buf, size) _write(fd, buf, (unsigned int)(size))
+
+#	define S_ISDIR(m) (((m) & _S_IFMT) == _S_IFDIR)
+#	define S_ISREG(m) (((m) & _S_IFMT) == _S_IFREG)
+#endif
+
 #ifndef O_BINARY
 #	define O_BINARY 0
 #endif

src/xz/file_io.h

@@ -18,6 +18,16 @@
 #	define IO_BUFFER_SIZE (BUFSIZ & ~7U)
 #endif
 
+#ifdef _MSC_VER
+	// The first one renames both "struct stat" -> "struct _stat64"
+	// and stat() -> _stat64(). The documentation mentions only
+	// "struct __stat64", not "struct _stat64", but the latter
+	// works too.
+#	define stat _stat64
+#	define fstat _fstat64
+#	define off_t __int64
+#endif
+
 
 /// is_sparse() accesses the buffer as uint64_t for maximum speed.
 /// The u32 and u64 members must only be access through this union