Adds a new CI job which checks that the compiler builds with
`--enable-debug` and tests that `needs-force-clang-based-tests` pass
(where cross-language LTO is tested).
With the exception of `tests/run-make/translation/test.rs`, which has a
syntax error.
The expected output in `rustdoc-error-lines/rmake.rs`'s required slight
tweaking.
The two `reproducible-build.rs` files need `// ignore-tidy-linelength`
because rustfmt produces lines longer than 100 chars, which tidy doesn't
like, yuk.
