Don't rely on the static global gs_perfCounter being already initialized when
wxStopWatch::DoStart() is called, this may not be the case if wxStopWatch
variable is global.
Work around this by wrapping the variable inside a function to ensure that it
is initialized before being used.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76986 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775