cmake build: Disable clangpchmanagerbackend and refactoringbackend

By default. Previously only the corresponding plugins were disabled, but
not even building the backends makes more sense.

Change-Id: I36d61869a3050f37da1f480dea89e7539dda599a
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangrefactoring/CMakeLists.txt

@@ -1,6 +1,5 @@
 add_qtc_plugin(ClangRefactoring
-  BUILD_DEFAULT OFF
-  CONDITION TARGET libclang
+  CONDITION TARGET libclang AND TARGET clangrefactoringbackend
   DEPENDS ClangSupport CPlusPlus
   PLUGIN_DEPENDS Core CppTools TextEditor ClangPchManager
   SOURCES ${TEST_SOURCES}