Reviewed the ODLocks removed at cbf1bb5, restored just two of them...

... as std::mutex instead.

One is the mutex for the set of all files.

Another is in Profiler.h, which is now back into CMakeLists because the header
is included in one place.  Maybe this utility will find more use again.

Restored one other but commented out, as not necessary now, but need might be
found to put it back again.

The class ODLock was a misnamed thing not specific to the on-demand manager but
used more widely as a thread synchronization utility, functioning as a mutex
object.  It was a mistake to remove all uses of it along with the rest of the
on-demand system.

src/FileFormats.cpp

@@ -320,6 +320,8 @@ static OSType sf_header_mactype(int format)
 
 #endif // __WXMAC__
 
+//std::mutex libSndFileMutex;
+
 int SFFileCloser::operator() (SNDFILE *sf) const
 {
    auto err = SFCall<int>(sf_close, sf);