* The dispatch_get_main_queue function doesn't exist anywhere (tested on iOS 5.1.1 - iOS 12, macOS 10.7 - 10.14), and when called from native code, it's always an inlined function, so just remove the call completely.
* Getting the _dispatch_main_q symbol from either the current address space, libSystem or libdispatch works fine everywhere. Looking up something in the current address space is costly (according to 'man dlsym'), so stop doing that: only look in libdispatch (since that's where the symbol actually is according to 'nm').
* I find no reason for the lock in DispatchQueue.MainQueue, nor does history reveal anything helpful, so I removed the lock.
* Not every old annotations have been migrated (work in progress, to be completed in another PR);
* Sanitation of the data files (e.g. removal of dupes and fixed, by Apple, entries) is done, but not automated (also a work in progress)
Even then this is immediately useful, i.e. better merged before 15.6 gets branched.
Pramit Mallick
Rolf Bjarne Kvinge
Sebastien Pouliot