Rust fixes for v6.18
Toolchain and infrastructure:
- Fix/workaround a couple Rust 1.91.0 build issues when sanitizers are
enabled due to extra checking performed by the compiler and an
upstream issue already fixed for Rust 1.93.0.
- Fix future Rust 1.93.0 builds by supporting the stabilized name for
the 'no-jump-tables' flag.
- Fix a couple private/broken intra-doc links uncovered by the future
move of pin-init to 'syn'.