I'm also not sure where “mir_egl_mesa_display_is_valid” comes from; I can't find it in the Mir codebase. It's possible that what you want to do is check for mir_connection_is_valid() there anyway.
I'm also not sure where “mir_egl_ mesa_display_ is_valid” comes from; I can't find it in the Mir codebase. It's possible that what you want to do is check for mir_connection_ is_valid( ) there anyway.