6794 added support for passing -package and -thread options to ocamlfind for C files.
oasis automatically adds "-thread" for ocaml files when they are flagged with "package(threads)". But it does it only for ocaml files and still flags C files with "package(X)" for every package, even though this is useless at the moment.
I guess this is more an oasis bug, but it will affect packages with C stubs using oasis and depending on threads. So it might be safer to revert 6794 from 4.02.2.