loplugin:unusedenumconstants update for new clang AST node

Change-Id: I5838f4fded09ad0f4eabc2dbf38ac2eb5c60777e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/170182
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

compilerplugins/clang/unusedenumconstants.cxx

@@ -271,6 +271,10 @@ walk_up:
     {
         goto walk_up;
     }
+    else if (isa<CXXDefaultInitExpr>(parent))
+    {
+        goto walk_up;
+    }
     else if (isa<UnresolvedLookupExpr>(parent)
             || isa<CompoundStmt>(parent))
     {