Auto merge of #41544 - alexcrichton:bump-bootstrap, r=brson

Update stage0 bootstrap compiler

We've got a freshly minted beta compiler, let's update to use that on nightly!
This has a few other changes associated with it as well

* A bump to the rustc version number (to 1.19.0)
* Movement of the `cargo` and `rls` submodules to their "proper" location in
  `src/tools/{cargo,rls}`. Now that Cargo workspaces support the `exclude`
  option this can work.
* Updates of the `cargo` and `rls` submodules to their master branches.
* Tweak to the `src/stage0.txt` format to be more amenable for Cargo version
  numbers. On the beta channel Cargo will bootstrap from a different version
  than rustc (e.g. the version numbers are different), so we need different
  configuration for this.
* Addition of `dev` as a readable key in the `src/stage0.txt` format. If present
  then stage0 compilers are downloaded from `dev-static.rust-lang.org` instead
  of `static.rust-lang.org`. This is added to accomodate our updated release
  process with Travis and AppVeyor.

src/tools/cargo

@@ -0,0 +1 @@
+Subproject commit fa7584c1495c2d9c04a6416f8e7b546abfa88a52

src/tools/rls

@@ -0,0 +1 @@
+Subproject commit 67babd2d63710444a3071dfd9184648fd85a6a3d

src/tools/tidy/src/main.rs

@@ -85,6 +85,8 @@ fn filter_dirs(path: &Path) -> bool {
         "src/liblibc",
         "src/vendor",
         "src/rt/hoedown",
+        "src/tools/cargo",
+        "src/tools/rls",
     ];
     skip.iter().any(|p| path.ends_with(p))
 }