iOS: Refactor iOS tool chain and kit auto detection

It was all done in one huge, unreadable method.
The refactoring along-side fixes the following:

- iOS tool chains were demoted to manual at start up because there
  was no tool chain factory that would auto detect them
- a QTC_CHECK failed because single Qt Versions could appear multiple
  times in the architecture->Qt version map, because each architecture
  is present in two abis (32-bit and 64-bit)

The refactoring also removes unneeded automatic conversion
from non-iOS Qt version to iOS Qt version, and removes considering GCC
toolchains (which were not handled anyhow, because only Clang
"platforms" were considered).

Change-Id: Ic9ae797646f159ed45959fc797990aa98f2136fb
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/ios/iosconfigurations.h

@@ -31,6 +31,7 @@
 #define IOSCONFIGURATIONS_H
 
 #include <projectexplorer/abi.h>
+#include <projectexplorer/toolchain.h>
 #include <utils/fileutils.h>
 
 #include <QObject>
@@ -44,6 +45,15 @@ QT_END_NAMESPACE
 namespace Ios {
 namespace Internal {
 
+class IosToolChainFactory : public ProjectExplorer::ToolChainFactory
+{
+    Q_OBJECT
+
+public:
+    QList<ProjectExplorer::ToolChain *> autoDetect(const QList<ProjectExplorer::ToolChain *> &existingToolChains) override;
+};
+
+
 class IosConfigurations : public QObject
 {
     Q_OBJECT