Fix HAVE_MPI undefined warnings (with -Wundef flag)
I am currently testing our extension module dune-xt
with the releases/2.8
branch of the core modules, and I am getting a lot of -Wundef
warnings from our config.h
.
I know that dune-common
does not use this warning flag, but since the contents of the config.h.cmake
file are included in the configs of all modules that depend on dune-common
, I suggest to fix this warning to allow dependent modules to use the -Wundef
flag.