Miscellaneous inlining improvements

Add `#[inline]` to a few trivial non-generic methods from a perf report
that otherwise wouldn't be candidates for inlining.

compiler/rustc_query_system/src/query/mod.rs

@@ -81,6 +81,7 @@ pub struct QuerySideEffects {
 }
 
 impl QuerySideEffects {
+    #[inline]
     pub fn is_empty(&self) -> bool {
         let QuerySideEffects { diagnostics } = self;
         diagnostics.is_empty()