osx fix

experiencing same build error on Mac OS X reported on trac.wxwidgets.org [#16329](http://trac.wxwidgets.org/ticket/16329)

applying changeset [76743](http://trac.wxwidgets.org/changeset/76743) -- or really doing a `git cherry-pick` of [this commit](https://github.com/wxWidgets/wxWidgets/commit/1a5b71210349cc45ff88e02ccf989f8fdb45254b) fixes the build error - but there were some merge conflicts to [resolve](https://github.com/smanders/wxWidgets/commit/115ee4f92c13b85e6d931397f9d4534c1fc8b746)