add test for invalid char

tests/compile-fail/match_char.rs

@@ -0,0 +1,8 @@
+fn main() {
+    assert!(std::char::from_u32(-1_i32 as u32).is_none());
+    match unsafe { std::mem::transmute::<i32, char>(-1) } {
+        'a' => {}, //~ERROR tried to interpret an invalid 32-bit value as a char: 4294967295
+        'b' => {},
+        _ => {},
+    }
+}