CMake: Enable switching between different temporary CMake configurations

This got broken when moving the BuildDirManager from the BuildConfiguration
into the Project itself.

As a side-effect this patch also fixes the persisting of cmake state.

Task-number: QTCREATORBUG-19075
Change-Id: I1fc696097b09f5285e67f20885eb1fa27504990b
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/cmakeprojectmanager/cmakeproject.cpp

@@ -160,11 +160,11 @@ CMakeProject::CMakeProject(const FileName &fileName) : Project(Constants::CMAKEM
             return;
 
         // Build configuration has switched:
-        // * Error out if the reader updates, can not happen since all BCs share a target/kit.
+        // * Check configuration if reader changes due to it not existing yet:-)
         // * run cmake without configuration arguments if the reader stays
         m_buildDirManager.setParametersAndRequestParse(
                     BuildDirParameters(bc),
-                    BuildDirManager::REPARSE_FAIL,
+                    BuildDirManager::REPARSE_CHECK_CONFIGURATION,
                     BuildDirManager::REPARSE_CHECK_CONFIGURATION);
     });