-export mingw_include=$mingw_top/include
-export mingw_lib=$mingw_top/lib
-export mingw_bin=$mingw_top/bin
+if [ "x${mingw_include}" == "x" ]; then
+ export mingw_include=$mingw_top/include
+fi
+if [ "x${mingw_lib}" == "x" ]; then
+ export mingw_lib=$mingw_top/lib
+fi
+if [ "x${mingw_bin}" == "x" ]; then
+ export mingw_bin=$mingw_top/bin
+fi