Comment (by Roland Haas):

hmm, would be nice if it told me what that invalid value was. Could you re-run with export VERBOSE=yes, please? That should show you the shell command that the build script tries to execute and thus the bad option value as well.

it really only ever should be 1. a number (incl. 1), 2. nothing (if make was called with -j without any options).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/1775/add-boost-to-et