Toolchain and infrastructure:

 - Do not export KASAN ODR symbols to avoid gendwarfksyms warnings.

 - Fix future Rust 1.86.0 (to be released 2025-04-03) x86_64 builds.

 - Clean future Rust 1.86.0 (to be released 2025-04-03) warning.

 - Fix future GCC 15 (to be released in a few months) builds.

 - Fix `rusttest` target in macOS.