cmake: REQUIRED packages HYPREConfig.cmake

[junghans]

When a package uses a mpi-enabled hypre, mpi is actually required, same for lapack, blas and OpenMP.

@osborn9

[cedricchevalier19]

Just an user comment on this: I think it's good to have the REQUIRED concept in the client but for packaging, with Spack for example, it should be better to have the REQUIRED keyword when doing the actual find_package in Hypre's own CMakeLists.txt. find_dependency should properly forward the REQUIRED and QUIET kewords (https://cmake.org/cmake/help/latest/module/CMakeFindDependencyMacro.html).
The advantage of this is if user asks for Hypre with OpenMP and OpenMP is not found, cmake will fail. For automatic installations it is a lot easier to fix fail at configure time than try to figure out why some features are missing later.

[osborn9]

Ok, so based on @cedricchevalier19 comment, since we are using the REQUIRED keyword within the find_package calls then these keywords should be correctly forwarded.

@junghans Are there instances when the find_dependency isn't behaving as expected?

[junghans]

It is mainly good practice, but you could construct a case where you e.g. compile a consumer code with a different compiler that doesn't support OpenMP and then hypre is looking for OpenMP and doesn't find. Throwing an error in these cases seem better.