2021 week 23: rebase off upstream

[adpaco-aws]

[adpaco-aws]

Merge conflict in compiler/rustc_interface/src/util.rs (where we redefine get_builtin_codegen_backend). Incoming change is empty so we keep our changes.

[adpaco-aws]

That did not work. The get_builtin_codegen_backend function got removed in this commit and the backend match is now done in get_codegen_backend which we extend for the gotoc case.

These changes have taken place in compiler/rustc_interface/src/util.rs: Compare old and new commits.

[adpaco-aws]

The new branch is main-152-2021-06-07