CI: replace compiletest-rs with trybuild

We use compiletest to run compile-fail tests but compiletest depends on compiler
internals so it breaks every now and then and requires nightly. With trybuild we
can also run compile-fail tests but it works on stable and it already has
reached version 1.0

tests/single.rs

@@ -1,19 +1,7 @@
-use std::path::PathBuf;
-
-use compiletest_rs::{common::Mode, Config};
+use trybuild::TestCases;
 
 #[test]
 fn ui() {
-    let mut config = Config::default();
-
-    config.mode = Mode::Ui;
-    config.src_base = PathBuf::from("ui/single");
-    config.target_rustcflags = Some(
-        "--edition=2018 -L target/debug/deps -Z unstable-options --extern rtfm --extern lm3s6965"
-            .to_owned(),
-    );
-    config.link_deps();
-    config.clean_rmeta();
-
-    compiletest_rs::run_tests(&config);
+    let t = TestCases::new();
+    t.compile_fail("ui/single/*.rs");
 }