Auto merge of #54223 - pnkfelix:issue-53764-uiify-run-pass, r=nikomatsakis

`ui`ify run-pass

This addresses the remainder of #53764 by first converting `src/test/run-pass` into another `ui`-style test suite, and then turning on `compare-mode=nll` for that new suite.

After this lands, we can address #54047 for the short term by moving all the `src/test/ui/run-pass` tests back to `src/test/run-pass`.

(Longer term, the compiler team's current (hypothetical sketch of a) plan (see [1][], [2][]) is unify all the tests by embedding these meta-properties like "// run-pass` into their headers explicitly and dropping the significance of their location on the file system.)

[1]: https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/subject/weekly.20meeting.202018-09-13/near/133889370
[2]: #54047 (comment)

Author: bors

src/bootstrap/test.rs

@@ -755,10 +755,11 @@ default_test_with_compare_mode!(Ui {
     compare_mode: "nll"
 });
 
-default_test!(RunPass {
+default_test_with_compare_mode!(RunPass {
     path: "src/test/run-pass",
     mode: "run-pass",
-    suite: "run-pass"
+    suite: "run-pass",
+    compare_mode: "nll"
 });
 
 default_test!(CompileFail {

src/test/run-pass-fulldeps/ast_stmt_expr_attr.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![allow(unused_imports)]
 // ignore-cross-compile
 
 #![feature(rustc_private)]