Auto merge of #46564 - Zoxc:rayon-queries, r=<try>

WIP: Parallelize passes using rayon

This builds on #46193 and #45912 and actually makes code run in parallel. This is not quite ready yet since `rustc` is not yet completely thread safe. It also uses a rough fork of rayon which uses fibers/stackful coroutines.

Author: bors

src/Cargo.lock

@@ -262,6 +262,10 @@ fn main() {
         }
     }
 
+    if env::var_os("RUSTC_PARALLEL_QUERIES").is_some() {
+        cmd.arg("--cfg").arg("parallel_queries");
+    }
+
     let color = match env::var("RUSTC_COLOR") {
         Ok(s) => usize::from_str(&s).expect("RUSTC_COLOR should be an integer"),
         Err(_) => 0,