Mention the issue number for the new mir-opt in the FIXMEs

Thanks for the suggestions, lcnr!

Co-authored-by: lcnr <rust@lcnr.de>

src/test/codegen/try_identity.rs

@@ -9,7 +9,7 @@ type R = Result<u64, i32>;
 
 // This was written to the `?` from `try_trait`, but `try_trait_v2` uses a different structure,
 // so the relevant desugar is copied inline in order to keep the test testing the same thing.
-// FIXME: while this might be useful for `r#try!`, it would be nice to have a MIR optimization
+// FIXME(#85133): while this might be useful for `r#try!`, it would be nice to have a MIR optimization
 // that picks up the `?` desugaring, as `SimplifyArmIdentity` does not.  See #85133
 #[no_mangle]
 pub fn try_identity(x: R) -> R {

src/test/mir-opt/simplify-arm.rs

@@ -30,7 +30,7 @@ fn from_error<T, E>(e: E) -> Result<T, E> {
 
 // This was written to the `?` from `try_trait`, but `try_trait_v2` uses a different structure,
 // so the relevant desugar is copied inline in order to keep the test testing the same thing.
-// FIXME: while this might be useful for `r#try!`, it would be nice to have a MIR optimization
+// FIXME(#85133): while this might be useful for `r#try!`, it would be nice to have a MIR optimization
 // that picks up the `?` desugaring, as `SimplifyArmIdentity` does not.  See #85133
 fn id_try(r: Result<u8, i32>) -> Result<u8, i32> {
     let x = match into_result(r) {

src/test/mir-opt/simplify_try.rs

@@ -15,7 +15,7 @@ fn from_error<T, E>(e: E) -> Result<T, E> {
 
 // This was written to the `?` from `try_trait`, but `try_trait_v2` uses a different structure,
 // so the relevant desugar is copied inline in order to keep the test testing the same thing.
-// FIXME: while this might be useful for `r#try!`, it would be nice to have a MIR optimization
+// FIXME(#85133): while this might be useful for `r#try!`, it would be nice to have a MIR optimization
 // that picks up the `?` desugaring, as `SimplifyArmIdentity` does not.  See #85133
 fn try_identity(x: Result<u32, i32>) -> Result<u32, i32> {
     let y = match into_result(x) {