Use gen blocks in the compiler instead of from_coroutine

compiler/rustc_hir_analysis/src/lib.rs

@@ -62,8 +62,8 @@ This API is completely unstable and subject to change.
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(assert_matches)]
-#![feature(coroutines)]
 #![feature(debug_closure_helpers)]
+#![feature(gen_blocks)]
 #![feature(if_let_guard)]
 #![feature(iter_from_coroutine)]
 #![feature(iter_intersperse)]