What this MR does / why does DuMux need it:
Add missing CMake guard for UMFPack to tracer tests Add header that is no longer automatically included with upcoming GCC and Clang versions.
What this MR does / why does DuMux need it:
Add missing CMake guard for UMFPack to tracer tests Add header that is no longer automatically included with upcoming GCC and Clang versions.