CMake: Make shadowBuildDirectory helper available

Make shadowBuildDirectory(...) a static method of CMakeBuildConfiguration.
That way it can be used by a future projectimporter.

Change-Id: I1b3ffc821ac9197aa5c90e2b78891df7a81a31dd
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>

src/plugins/cmakeprojectmanager/cmakebuildconfiguration.h

@@ -77,6 +77,10 @@ public:
     void resetData();
     bool persistCMakeState();
 
+    static Utils::FileName
+    shadowBuildDirectory(const Utils::FileName &projectFilePath, const ProjectExplorer::Kit *k,
+                         const QString &bcName, BuildConfiguration::BuildType buildType);
+
 signals:
     void errorOccured(const QString &message);