CVE-2023-1521: sccache vulnerable to privilege escalation if server is run as root

The vulnerability stems from the client sending its environment variables (including LD_PRELOAD) to the server during compilation requests. The code in src/commands.rs lines 371-376 explicitly includes env_vars in the Compile request struct. A FIXME comment in src/cmdline.rs:279 acknowledges the risk of not sanitizing LD_PRELOAD. The server's execution environment inherits these variables, enabling privilege escalation when running as root. The function responsible for constructing and sending these tainted environment variables is the root cause.