make Windows cross compile work

depends/config.site.in

@@ -52,6 +52,15 @@ if test x@host_os@ = xdarwin; then
   PORT=no
 fi
 
+if test x@host_os@ = xmingw32; then
+  if test -z $with_qt_incdir; then
+    with_qt_incdir=$depends_prefix/include
+  fi
+  if test -z $with_qt_libdir; then
+    with_qt_libdir=$depends_prefix/lib
+  fi
+fi
+
 PATH=$depends_prefix/native/bin:$PATH
 PKG_CONFIG="$(which pkg-config) --static"