Rollup of 5 pull requests

[Centril]

Successful merges:

• Use libunwind from llvm-project submodule for musl targets #63173 (Use libunwind from llvm-project submodule for musl targets)
• Opaque builtin derive macros #63462 (Opaque builtin derive macros)
• Suggest Rust 2018 on <expr>.await with no such field #63539 (Suggest Rust 2018 on <expr>.await with no such field)
• Feature gate 'yield $expr?' pre-expansion #63545 (Feature gate 'yield $expr?' pre-expansion)
• libcore: more cleanups using #![feature(associated_type_bounds)] #63584 (libcore: more cleanups using #![feature(associated_type_bounds)])

Failed merges:

r? @ghost