Package rust: Information

- New version (1.51.0).
- Use llvm12.0.
- Security fixes:
  + CVE-2020-36323 rust: optimization for joining strings can cause uninitialized bytes to be exposed
  + CVE-2021-28876 rust: panic safety issue in Zip implementation
  + CVE-2021-28878 rust: memory safety violation in Zip implementation when next_back() and next() are used together
  + CVE-2021-28879 rust: integer overflow in the Zip implementation can lead to a buffer overflow
  + CVE-2021-31162 rust: double free in Vec::from_iter function if freeing the element panics

- New version (1.50.0).

- New version (1.49.0).
- Use clang.