Fix gzopen_w() type and add #include for the type.

gzguts.h

@@ -27,6 +27,10 @@
 #endif
 #include <fcntl.h>
 
+#ifdef _WIN32
+#  include <stddef.h>
+#endif
+
 #if defined(__TURBOC__) || defined(_MSC_VER) || defined(_WIN32)
 #  include <io.h>
 #endif

gzlib.c

@@ -275,7 +275,7 @@ gzFile ZEXPORT gzdopen(fd, mode)
 /* -- see zlib.h -- */
 #ifdef _WIN32
 gzFile ZEXPORT gzopen_w(path, mode)
-    const w_char *path;
+    const wchar_t *path;
     const char *mode;
 {
     return gz_open(path, -2, mode);

zlib.h

@@ -1733,7 +1733,7 @@ ZEXTERN int            ZEXPORT inflateUndermine OF((z_streamp, int));
 ZEXTERN int            ZEXPORT inflateResetKeep OF((z_streamp));
 ZEXTERN int            ZEXPORT deflateResetKeep OF((z_streamp));
 #if defined(_WIN32) && !defined(Z_SOLO)
-ZEXTERN gzFile         ZEXPORT gzopen_w OF((const w_char *path,
+ZEXTERN gzFile         ZEXPORT gzopen_w OF((const wchar_t *path,
                                             const char *mode));
 #endif