CMake: Do not map all unknown build target types to "ExecutableType"

There is UtilityType now, so use that if there is no executable being
generated.

Change-Id: I9e8d512077b8352ec056b49c8db03644482b8fbc
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/cmakeprojectmanager/cmakeproject.h

@@ -70,7 +70,7 @@ class CMAKE_EXPORT CMakeBuildTarget
 public:
     QString title;
     QString executable; // TODO: rename to output?
-    TargetType targetType;
+    TargetType targetType = UtilityType;
     QString workingDirectory;
     QString sourceDirectory;
     QString makeCommand;