Update outdated comment

The highest-priority item is the *first* in the list, not the last.
See [this code][1] for more.

[this code]: https://github.com/rust-lang/rust/blob/0e63af5da3400ace48a0345117980473fd21ad73/compiler/rustc_mir_build/src/build/matches/mod.rs#L1334-L1335

Author: camelid

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -1226,9 +1226,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// this point, the input candidates have been fully simplified,
     /// and so we know that all remaining match-pairs require some
     /// sort of test. To decide what test to perform, we take the highest
-    /// priority candidate (last one in the list) and extract the
-    /// first match-pair from the list. From this we decide what kind
-    /// of test is needed using [`Builder::test`], defined in the
+    /// priority candidate (the first one in the list, as of January 2021)
+    /// and extract the first match-pair from the list. From this we decide
+    /// what kind of test is needed using [`Builder::test`], defined in the
     /// [`test` module](mod@test).
     ///
     /// *Note:* taking the first match pair is somewhat arbitrary, and