Compiletest: pass -Zui-testing to rustc

This is the dual of Rust-GPU/rust-gpu#447

Author: LegNeato

tests/compiletests/src/main.rs

@@ -122,6 +122,7 @@ impl Runner {
                 "-Zunstable-options",
                 "-Zcrate-attr=no_std",
                 "-Zcrate-attr=feature(abi_ptx)",
+                "-Zui-testing",
             ]
             .join(" ")
         }

tests/compiletests/ui/lang/compile_fail.stderr

@@ -1,10 +1,10 @@
 error[E0433]: failed to resolve: use of unresolved module or unlinked crate `std`
- --> $DIR/compile_fail.rs:5:14
-  |
-5 |     let _s = std::fs::File::create("foo.txt");
-  |              ^^^ use of unresolved module or unlinked crate `std`
-  |
-  = help: you might be missing a crate named `std`
+  --> $DIR/compile_fail.rs:5:14
+   |
+LL |     let _s = std::fs::File::create("foo.txt");
+   |              ^^^ use of unresolved module or unlinked crate `std`
+   |
+   = help: you might be missing a crate named `std`
 
 error: aborting due to 1 previous error