Adapt m4 macro for openmp

Description

The macro did not test properly compilation and linking of OpenMP code, only linking. Now use the code from the autoconf source, slightly adapted (test -qopenmp for intel, define HAVE_OPENMP macro as used in the code).

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Adapt m4 macro for openmp

Checklist

• I have checked that my code follows the [Octopus coding standards](http://octopus-code.org/wiki/Developers:Coding_standard