RunConfiguration: Introduce buildSystemTarget()

Introduce a method that maps a RunConfiguration to the build system target
that created the executable.

Implement the method in all RunConfigurations where that makes sense (e.g.
no CustomExecutables).

Change-Id: Ifaac859c2cd9b2806a0d7c185b2239312a67752a
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/ios/iosrunconfiguration.h

@@ -68,6 +68,8 @@ public:
     bool fromMap(const QVariantMap &map) override;
     QVariantMap toMap() const override;
 
+    QString buildSystemTarget() const final;
+
 protected:
     IosRunConfiguration(ProjectExplorer::Target *parent, IosRunConfiguration *source);