Same as for the Clang Static Analyzer, so move the implementation into the base
class and use it.

This has gone unnoticed so far because it looks like that the error diagnostic
from the bug report can be extracted with libclang (as shown in the info bar),
but is not printed from libclang or clang.exe itself.

Change-Id: I5b714ba374c5fdefe234faf012a3515e96c9a08c
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>