CONFIG: restrict wmakeLnInclude to header/template files

- source-code (.c, .cpp etc) only adds to clutter in the lnInclude
  directory

applications/test/00-dummy/library/dummy/dummyMpiLib.cpp

@@ -0,0 +1,46 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2020 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "dummyLib.H"
+#include <iostream>
+
+// * * * * * * * * * * * * * * Global Functions  * * * * * * * * * * * * * * //
+
+bool Foam::Detail::dummyLib::hasMPI()
+{
+    return false;
+}
+
+
+bool Foam::Detail::dummyLib::printMPI()
+{
+    std::cout << "Compiled without mpi\n";
+    return true;
+}
+
+
+// ************************************************************************* //