Android: Use less direct access to the qmake build step

Instead of qobject_cast use the reacently introduced virtual function
BuildConfiguration::regenerateBuildFiles() to trigger the necessary
work in the qmake case.

Change-Id: Ie5fd36550b5bad8c5f3f8bb1e2a3a16843f8f5b7
Reviewed-by: Vikas Pachdha <vikas.pachdha@qt.io>

src/plugins/projectexplorer/buildconfiguration.h

@@ -96,6 +96,7 @@ public:
 
     void prependCompilerPathToEnvironment(Utils::Environment &env) const;
     static void prependCompilerPathToEnvironment(Kit *k, Utils::Environment &env);
+    void updateCacheAndEmitEnvironmentChanged();
 
 signals:
     void environmentChanged();
@@ -105,7 +106,6 @@ signals:
 
 protected:
     virtual void initialize(const BuildInfo *info);
-    void updateCacheAndEmitEnvironmentChanged();
 
 private:
     void emitBuildDirectoryChanged();