Add blank lines after module-level //! comments.

Most modules have such a blank line, but some don't. Inserting the blank
line makes it clearer that the `//!` comments are describing the entire
module, rather than the `use` declaration(s) that immediately follows.

compiler/rustc_mir_transform/src/ctfe_limit.rs

@@ -1,5 +1,6 @@
 //! A pass that inserts the `ConstEvalCounter` instruction into any blocks that have a back edge
 //! (thus indicating there is a loop in the CFG), or whose terminator is a function call.
+
 use crate::MirPass;
 
 use rustc_data_structures::graph::dominators::Dominators;

compiler/rustc_mir_transform/src/inline.rs

@@ -1,4 +1,5 @@
-//! Inlining pass for MIR functions
+//! Inlining pass for MIR functions.
+
 use crate::deref_separator::deref_finder;
 use rustc_attr::InlineAttr;
 use rustc_hir::def::DefKind;

compiler/rustc_mir_transform/src/lint.rs

@@ -1,6 +1,7 @@
 //! This pass statically detects code which has undefined behaviour or is likely to be erroneous.
 //! It can be used to locate problems in MIR building or optimizations. It assumes that all code
 //! can be executed, so it has false positives.
+
 use rustc_data_structures::fx::FxHashSet;
 use rustc_index::bit_set::BitSet;
 use rustc_middle::mir::visit::{PlaceContext, Visitor};