Update ui tests

Author: GuillaumeGomez

src/librustc/error_codes.rs

@@ -1705,12 +1705,9 @@ Conflicting representation hints have been used on a same item.
 
 Erroneous code example:
 
-```compile_fail,E0566
-# #![deny(warnings)]
-# fn main() {
-#[repr(u32, u64)] // error!
+```
+#[repr(u32, u64)] // warning!
 enum Repr { A }
-# }
 ```
 
 In most cases (if not all), using just one representation hint is more than

src/test/ui/conflicting-repr-hints.stderr

@@ -66,3 +66,4 @@ LL | | }
 
 error: aborting due to 8 previous errors
 
+For more information about this error, try `rustc --explain E0566`.

src/test/ui/feature-gates/feature-gate-repr-simd.stderr

@@ -26,4 +26,5 @@ LL | #[repr(simd)]
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0658`.
+Some errors have detailed explanations: E0566, E0658.
+For more information about an error, try `rustc --explain E0566`.