ENH: provide openmp compile and link flags.

- the USE_OMP preprocessor symbol is also defined with the openmp
  compile flag to allow conditional compilation of openmp-specific
  code.

applications/test/openmp/Test-openmp.C

@@ -0,0 +1,69 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2017 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+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/>.
+
+Description
+    Simple test program for compiling/running openmp
+
+\*---------------------------------------------------------------------------*/
+
+#include <cstdio>
+#include <cstdlib>
+#include <iostream>
+
+#ifdef USE_OMP
+#include <omp.h>
+#endif
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+// Main program:
+
+int main(int argc, char *argv[])
+{
+    int nThreads, threadId;
+
+// Fork threads with their own copies of variables
+#ifdef USE_OMP
+#pragma omp parallel private(nThreads, threadId)
+    {
+        threadId = omp_get_thread_num();
+        nThreads = omp_get_num_threads();
+
+        // Printf rather than cout to ensure that it emits in one go
+        printf("Called from thread = %d\n", threadId);
+
+        // Master thread
+        if (threadId == 0)
+        {
+            // Printf rather than cout to ensure that it emits in one go
+            printf("Number of threads = %d\n", nThreads);
+        }
+    }
+#else
+    std::cout << "Compiled without openmp!\n";
+#endif
+
+    return 0;
+}
+
+
+// ************************************************************************* //