lang/rust: Update to 1.78.0

While here, disable RUST_BACKTRACE on ppc64le only

Announce: https://blog.rust-lang.org/2024/05/02/Rust-1.78.0.html
ChangeLog: https://github.com/rust-lang/rust/releases/tag/1.78.0

PR: 278834
Tested by: pkubaj,mikael