<blockquote>
<p>I switched gcc from 5.3 to 4.9 for gcc_5.3 will not support OpenMp anymore....</p>
</blockquote>

<p>Can you tell me more of what you mean here?  I can't find any evidence that newer GCC is dropping support for OpenMP; maybe I have misunderstood something?</p>

<p>If you've switched compilers, you should definitely remove CMakeCache.txt from your build directory and reconfigure with cmake (maybe you did this, I don't know).  Another thing to do might be to paste the output of</p>

<pre><code>VERBOSE=1 make
</code></pre>

<p>and that will produce the actual linker command that is used, which might give us more information about what is going wrong.  It will be a lot of output though... :)</p>

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