Rollup merge of #108694 - est31:backticks_matchmaking_comments, r=Nilstrieb

Match unmatched backticks in compiler/ comments

r? ``@Nilstrieb`` as per [advice](https://github.com/rust-lang/rust/pull/108685#issuecomment-1453018499)

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -415,7 +415,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
     /// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x }
     /// ```
     ///
-    /// Here we would be invoked with `fr = 'a` and `outlived_fr = `'b`.
+    /// Here we would be invoked with `fr = 'a` and `outlived_fr = 'b`.
     pub(crate) fn report_region_error(
         &mut self,
         fr: RegionVid,

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -889,7 +889,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// from a universe it can't name; at present, the only way for
     /// this to be true is if `scc` outlives `'static`. This is
     /// actually stricter than necessary: ideally, we'd support bounds
-    /// like `for<'a: 'b`>` that might then allow us to approximate
+    /// like `for<'a: 'b>` that might then allow us to approximate
     /// `'a` with `'b` and not `'static`. But it will have to do for
     /// now.
     fn add_incompatible_universe(&mut self, scc: ConstraintSccIndex) {

compiler/rustc_borrowck/src/region_infer/values.rs

@@ -235,7 +235,7 @@ pub(crate) struct RegionValues<N: Idx> {
     free_regions: SparseBitMatrix<N, RegionVid>,
 
     /// Placeholders represent bound regions -- so something like `'a`
-    /// in for<'a> fn(&'a u32)`.
+    /// in `for<'a> fn(&'a u32)`.
     placeholders: SparseBitMatrix<N, PlaceholderIndex>,
 }