osgeo4w: add missing library (see https://trac.osgeo.org/grass/ticket/2959)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@68144 15284696-431f-4ddb-bdfa-cd5b030d7da7

mswindows/osgeo4w/package.sh

@@ -254,6 +254,7 @@ if [ -n "$PACKAGE_PATCH" ]; then
 	/mingw${MINGW_POSTFIX}/bin/libsystre-0.dll \
 	/mingw${MINGW_POSTFIX}/bin/libtre-5.dll \
         /mingw${MINGW_POSTFIX}/bin/zlib1.dll \
+        /mingw${MINGW_POSTFIX}/bin/libstdc++-6.dll \
 	apps/grass/grass-$VERSION/bin
     cp -uv /mingw${MINGW_POSTFIX}/etc/fonts/fonts.conf \
 	apps/grass/grass-$VERSION/etc