Print diagnostic groups as part of the LLVM printer in the same manner as the
Swift one does, always. Make `-print-diagnostic-groups` an inert option, since we
always print diagnostic group names with the `[#GroupName]` syntax.
As part of this, we no longer render the diagnostic group name as part
of the diagnostic *text*, instead leaving it up to the diagnostic
renderer to handle the category appropriately. Update all of the tests
that were depending on `-print-diagnostic-groups` putting it into the
text to instead use the `{{documentation-file=<file name>}}`
diagnostic verification syntax.
The concurrency runtime now deploys back to macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, which corresponds to the 5.1 release of the stdlib.
Adjust macro usages accordingly.
