attempt to make a minimal example work

compiler/rustc_const_eval/src/lib.rs

@@ -20,6 +20,7 @@ Rust MIR: a lowered representation of Rust.
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![feature(yeet_expr)]
+#![feature(if_let_guard)]
 #![feature(is_some_and)]
 #![recursion_limit = "256"]