Fix the remaning clang thread safety warnings in WTF::DataMutex.
The goal of this patch is to reduce the number of warnings in the
GStreamer codebase. Whether DataMutex should be deprecated in favor of
Locker with the clang TSA annotations is outside of the scope of this
Created attachment 430731 [details]
Committed r278558 (238556@main): <https://commits.webkit.org/238556@main>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 430731 [details].