Use do yeet () and do yeet _ instead of None? and Err(_)? in compiler

This prevents breakage when `?` no longer skews inference.

compiler/rustc_expand/src/lib.rs

@@ -12,6 +12,7 @@
 #![feature(proc_macro_internals)]
 #![feature(proc_macro_span)]
 #![feature(try_blocks)]
+#![feature(yeet_expr)]
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(internal_features)]