Rust 1.15 release status

For BSD platforms, beta has a problem when rustbuild is used. rustbuild makes assomption that “make” is GNU-make, but under BSD it isn’t the case.

It is corrected in nightly by:

The first PR contains the fix for make, and corrects also others build problems specific to OpenBSD. The second PR polish some cases for make, when makefiles are used (the first PR didn’t update that).