Auto merge of #36203 - petrochenkov:uvsdot, r=nrc

Replace `_, _` with `..` in patterns

This is how https://github.com/rust-lang/rust/issues/33627 looks in action.

Looks especially nice in leftmost/rightmost positions `(first, ..)`/`(.., last)`.
I haven't touched libsyntax intentionally because the feature is still unstable.

diff --cc src/librustc/session/config.rs
Simple merge

diff --cc src/librustc_driver/lib.rs
Simple merge

diff --cc src/librustc_metadata/creader.rs
Simple merge

diff --cc src/librustc_mir/transform/qualify_consts.rs
Simple merge

diff --cc src/librustc_save_analysis/dump_visitor.rs
Simple merge

diff --cc src/librustc_save_analysis/lib.rs
index f32baf30ff42e4517c24ec4790eb61f381c05b0b,f69edea047e311fc61d2df449c189fd8ac2691ee..04cd72ac2d3647de31dc91b94bc15fc5762b2b89
--- 1/src/librustc_save_analysis/lib.rs
--- 2/src/librustc_save_analysis/lib.rs
+++ b/src/librustc_save_analysis/lib.rs
@@@ -224,10 -216,9 +225,10 @@@ impl<'l, 'tcx: 'l> SaveContext<'l, 'tcx
                      qualname: qualname,
                      scope: self.enclosing_scope(item.id),
                      variants: def.variants.iter().map(|v| v.node.data.id()).collect(),
 +                    visibility: From::from(&item.vis),
                  }))
              }
-             ast::ItemKind::Impl(_, _, _, ref trait_ref, ref typ, _) => {
+             ast::ItemKind::Impl(.., ref trait_ref, ref typ, _) => {
                  let mut type_data = None;
                  let sub_span;