Fix checking for GTK+ 3.0 in configure.

Update gtk-3.0.m4 to work correctly with gthread module and regenerate
configure using the new version of this file.

Closes #15319.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74475 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775