fixes "error: macro "ftell" requires 3 arguments, but only 1 given" build error

--- libtiff/tiffiop.h
+++ libtiff/tiffiop.h
@@ -270,7 +270,7 @@
   Windows read/write APIs support only 'unsigned int' rather than 'size_t'.
   Windows off_t is only 32-bit, even in 64-bit builds.
 */
-#if defined(HAVE_FSEEKO)
+#if defined(__WIN32__) /* probably more checks are required __MSVCRT_VERSION__, etc. */
 /*
   Use fseeko() and ftello() if they are available since they use
   'off_t' rather than 'long'.  It is wrong to use fseeko() and