Rollup merge of rust-lang#45887 - xfix:assert-eq-trailling-comma, r=dtolnay

Allow a trailling comma in assert_eq/ne macro

From Rust beginners IRC:

<???> It sure does annoy me that assert_eq!() does not accept a trailing comma after the last argument.
<???> ???: File an issue against https://github.com/rust-lang/rust and CC @rust-lang/libs

Figured that might as well submit it. Will become insta-stable after merging (danger zone).

cc @rust-lang/libs

Author: kennytm

src/libcore/macros.rs

@@ -120,6 +120,9 @@ macro_rules! assert_eq {
             }
         }
     });
+    ($left:expr, $right:expr,) => ({
+        assert_eq!($left, $right)
+    });
     ($left:expr, $right:expr, $($arg:tt)+) => ({
         match (&($left), &($right)) {
             (left_val, right_val) => {
@@ -168,6 +171,9 @@ macro_rules! assert_ne {
             }
         }
     });
+    ($left:expr, $right:expr,) => {
+        assert_ne!($left, $right)
+    };
     ($left:expr, $right:expr, $($arg:tt)+) => ({
         match (&($left), &($right)) {
             (left_val, right_val) => {