Move location of mod query_impl.

This:
- reduces the amount of stuff inside `define_queries!`
- makes `define_queries!` look more like `define_callbacks!`

Also, I want to improve the formatting of `define_queries!` and this
will avoid one level of indentation.

Author: nnethercote

compiler/rustc_query_impl/src/lib.rs

@@ -63,7 +63,9 @@ pub fn query_system<'tcx>(
     }
 }
 
-rustc_middle::rustc_with_all_queries! { define_queries! }
+mod query_impl {
+    rustc_middle::rustc_with_all_queries! { define_queries! }
+}
 
 pub fn provide(providers: &mut rustc_middle::util::Providers) {
     providers.hooks.alloc_self_profile_query_strings =

compiler/rustc_query_impl/src/plumbing.rs

@@ -350,7 +350,8 @@ macro_rules! define_queries {
         // Non-queries are unused here.
         non_queries { $($_:tt)* }
     ) => {
-        pub(crate) mod query_impl { $(pub(crate) mod $name {
+        // This macro expects to be expanded into `mod query_impl` in the crate root.
+        $(pub(crate) mod $name {
             use super::*;
             use rustc_middle::query::erase::{self, Erased};
 
@@ -585,5 +586,5 @@ macro_rules! define_queries {
         }
 
         pub(crate) use for_each_query_vtable;
-    }}
+    }
 }