devel/rust-analyzer: mark as LTO_UNSAFE

rust-analyzer won't run (repeatedly terminated with signal 6) when
called from VSCode's rust-analyzer extension.

Error messages from rust-analyzer extension are as follows:
[Info - 17:39:30] Connection to server got closed. Server will restart.
[Info - 17:39:31] Connection to server got closed. Server will restart.
[Info - 17:39:31] Connection to server got closed. Server will restart.
[Info - 17:39:32] Connection to server got closed. Server will restart.
[Error - 17:39:32] The Rust Analyzer Language Server server crashed 5 times in the last 3 minutes. The server will not be restarted. See the output for more information.

Turning off LTO appears to work around the issue.

PR: 272291
Approved by: mikael