Xcode 11 doesn't support anything below iOS 7.0 (the linker will automatically
change the deployment target to 7.0), so we need to drop support as well
(since our native bits will be targetting iOS 7.0, and we can't change that).
https://github.com/xamarin/xamarin-macios/issues/6213
This won't affect device tests on the bots (because those already set LLVM
manually when testing Release), but it becomes less confusing when trying to
reproduce any problems locally, since now the project configuration on disk
matches the tested configuration.
Rolf Bjarne Kvinge
Alexander Köplinger
Manuel de la Pena