CppTools: Fix qbs build.

Change-Id: I92157e91f288a7abdaf3c8c3cf97cbff1d2872f0
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/cpptools.qbs

@@ -102,6 +102,8 @@ QtcPlugin {
         "symbolsfindfilter.h",
         "uicodecompletionsupport.cpp",
         "uicodecompletionsupport.h",
+        "builtinindexingsupport.cpp",
+        "builtinindexingsupport.h"
     ]
 
     Group {