Install `.oct-config` file for BISTs extracted from C++ sources?

After hg id 6dbb7356d83b, tests are run with the encoding that is set for the directory in which they are stored.

This should be working correctly for tests that are extracted from .m files. So test XYZ should be working even if XYZ.m is encoded differently from the global .m file encoding (as long as there is a .oct-config defining the correct encoding in the same folder or the correct dir_encoding was set otherwise).

It might be worth adding .oct-config files to the folders with the tests that the build system extracts from C++ sources.
Maybe, we could add .oct-config files to all of the folders that contain sources with BISTs in the repository. The build system could maybe copy those files when it extracts the BISTs from the sources.
But I don’t know how that would be done.

Any ideas or opinions?