since we still support g++-7, where filesystem is marked experimental,
we introduce a wrapper header and expose the namespace to use
as Opm::filesystem.
for gcc we unconditionally link with libstdc++fs in the python bindings.
the setup.py stuff links as c code, not c++ code, so it is not
automatically added on any gcc version. this might prove unportable
later.
That is the way it is done in other modules, too. We need this
at least for libecl as this target is used in opm-common_LIBRARIES
and not defined if there was no find_package(ecl) call. That call
is now made during execution of find_package_deps(opm-common).
use pure config mode.
we no longer compile a test application for the libraries,
however checks have been tightened by making sure version of
all opm modules are the same.
this allows for putting prereqs directly in the module repositories
