We support building against newer GTK+ version and using an older
one at runtime, so we must provide our implementations of these
functions even if GTK_CHECK_VERSION would indicate the function is
already available in GTK+.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67319 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775