Comment (by Steven R. Brandt):

I had the mistaken belief that "inline" was equivalent to "static inline." I've update the repo (https://bitbucket.org/stevenrbrandt/wvuthorns_diagnostics) to use static inline.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/1974/add-wvuthorns_diagnostics-to-the-et