Enable warning flags on Mac builds of MFEM#2

Merged

tzanio merged 9 commits intov2.0from

warnings-flags-tweak

Nov 6, 2021

Commits on May 31, 2021

Commits on Jun 4, 2021

Enable the "-pedantic -Wall -Werror" flags on Mac.
v-dobrev
committed

Commits on Sep 2, 2021