Comment (by Roland Haas):

Pull request to test for C++11 math for isnan is here: https://bitbucket.org/cactuscode/cactus/pull-requests/152

This is probably better than trying to rely on feature test macros since those may not really tell the truth due to bugs in c++ libraries.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2663/add-an-notice-about-minimum-intel-gcc