Rename Abi::MacOS/GenericMacFlavor to DarwinOS/GenericDarwinFlavor

This makes clear that the ABI encompasses all Darwin platforms (macOS,
iOS, tvOS, watchOS) in the wake of the OS X to macOS rename, and would
have been more technically correct anyways since ABIs are far below the
"macOS" parts of our favorite desktop Unix operating system.

Change-Id: I16d1477f44ffe70e5d8cddd67199a1602ba6fd97
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/ios/iosqtversion.cpp

@@ -86,7 +86,7 @@ QList<Abi> IosQtVersion::detectQtAbis() const
     for (int i = 0; i < abis.count(); ++i) {
         abis[i] = Abi(abis.at(i).architecture(),
                       abis.at(i).os(),
-                      Abi::GenericMacFlavor,
+                      Abi::GenericDarwinFlavor,
                       abis.at(i).binaryFormat(),
                       abis.at(i).wordWidth());
     }