loplugin:constantparam

and tweak the plugin to handle a crash seen with clang-9

Change-Id: Ie1ccf80c16a20dbca58e5bd081af13f75cf5ac8f
Reviewed-on: https://gerrit.libreoffice.org/75850
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

compilerplugins/clang/constantparam.cxx

@@ -168,9 +168,10 @@ std::string ConstantParam::getCallValue(const Expr* arg)
     }
     arg = arg->IgnoreParenCasts();
     // ignore this, it seems to trigger an infinite recursion
-    if (isa<UnaryExprOrTypeTraitExpr>(arg)) {
+    if (isa<UnaryExprOrTypeTraitExpr>(arg))
         return "unknown1";
-    }
+    if (arg->isValueDependent())
+        return "unknown2";
     APSInt x1;
     if (compat::EvaluateAsInt(arg, x1, compiler.getASTContext()))
     {