CMake: Make sure there is a "clean" target

Change-Id: I9e3eb49b7f5a2d7d5c89a53969c4703b3ce99330
Reviewed-by: Cristian Adam <cristian.adam@gmail.com>
Reviewed-by: Niels Weber <niels.weber@theqtcompany.com>

src/plugins/cmakeprojectmanager/cmakecbpparser.cpp

@@ -177,6 +177,16 @@ bool CMakeCbpParser::parseCbpFile(Kit *kit, const QString &fileName, const QStri
         sortFiles();
 
         fi.close();
+
+        // There is always a clean target:
+        CMakeBuildTarget cleanTarget;
+        cleanTarget.title = QLatin1String("clean");
+        cleanTarget.targetType = UtilityType;
+        cleanTarget.workingDirectory = m_buildDirectory;
+        cleanTarget.sourceDirectory = m_sourceDirectory;
+
+        m_buildTargets.append(cleanTarget);
+
         return true;
     }
     return false;