When specifying NO_DEFAULT_PATH, we have to specify include and lib
manually to find the headers and libraries. This commit does this
for FindParMETIS and FindPTScotch
Previously we added (PAR)METIS_INCLUDE_DIRS to CMAKE_REQUIRED_INCLUDES
even if these directories were not found and set to
(PAR)METIS_INCLUDE_DIR-NOTFOUND. Now we test whether they are found and only
use them in this case.
for me, 4292de413f lead to linker errors
if the sequential metis library was required (and the parallel is not
installed). see e.g.,
http://www.opm-project.org/CDash/viewBuildError.php?buildid=41290
The reason for this is a partial clash in the variable names which are
used by both modules. With this PR, the FindParMETIS module does not
write to any variables that are prefixed by "METIS_".
The AMG within dune-istl issues a warning if ParMETIS is not available.
The reason is that it uses ParMETIS or the ParMETIS bindings of PT-Scotch
to redistribute the load on the coarse levels. Even with an installed and
found PT-Scotch we need to adapt the include path and the libraries linked
to make it work.
Therefore this commit adds a module for searching for ParMETIS and activates
it whenever dune-istl is a dependency. With this the warning about missing
ParMETIS for flow_cp vanishes.
