Merge branch 'classnametest-no-demngling-fallback' into 'master'

ref:core/dune-common Run the classnametest is now run two times:

-   classnametest-demangled: skipped if __cxa_demangle() is missing
-   classnametest-fallback: an exit-status of 1 (resulting from failed checks
    expecting demangling) is still considered successfull, though anything
    else (e.g. segfault) will fail the test.

Closes: [#160]

See merge request [!666]

  [#160]: gitlab.dune-project.org/NoneNone/issues/160
  [!666]: gitlab.dune-project.org/core/dune-common/merge_requests/666


Closes #160