CMake compilation error with MPI_C and SUNDIALS

[mikekryjak]

The recent SUNDIALS update made it necessary to add the C language to the project line in the Hermes-3 cmake script (see bendudson/hermes-3@7407e35). I'm leaving this here in case this information is useful to someone.

[Steven-Roberts]

Just seeing this issue now. Is this still the case after this PR was merged? In particular, with this change https://github.com/boutproject/BOUT-dev/pull/2922/files#diff-3c300e85313a4acb4aa412b9d561a30fd081396a05de144d624ceec30e387c5dR300

[mikekryjak]

Yes, we are using this commit: d7f8807

You can see that the changes are there:

BOUT-dev/cmake/SetupBOUTThirdParty.cmake

Lines 300 to 301 in d7f8807

	enable_language(C)
	find_package(SUNDIALS REQUIRED)