Add ui test for incompatible_msrv lint

Author: GuillaumeGomez

tests/ui/incompatible_msrv.rs

@@ -0,0 +1,18 @@
+#![warn(clippy::incompatible_msrv)]
+#![feature(custom_inner_attributes)]
+#![clippy::msrv = "1.10.0"]
+
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+
+fn foo() {
+    let mut map: HashMap<&str, u32> = HashMap::new();
+    // Stable since 1.10, so should not warn.
+    assert_eq!(map.entry("poneyland").key(), &"poneyland");
+    if let Entry::Vacant(v) = map.entry("poneyland") {
+        v.into_key();
+        //~^ ERROR: bla
+    }
+}
+
+fn main() {}