Add regression tests

src/test/ui/macros/assert-eq-macro-msg.rs

+// run-fail
+// error-pattern:panicked at 'assertion failed: `(left == right)`
+// error-pattern: left: `2`
+// error-pattern:right: `3`: 1 + 1 definitely should be 3'
+// ignore-emscripten no processes
+
+fn main() {
+    assert_eq!(1 + 1, 3, "1 + 1 definitely should be 3");
+}

src/test/ui/macros/assert-matches-macro-msg.rs

+// run-fail
+// error-pattern:panicked at 'assertion failed: `(left matches right)`
+// error-pattern: left: `2`
+// error-pattern:right: `3`: 1 + 1 definitely should be 3'
+// ignore-emscripten no processes
+
+#![feature(assert_matches)]
+
+fn main() {
+    assert_matches!(1 + 1, 3, "1 + 1 definitely should be 3");
+}

src/test/ui/macros/assert-ne-macro-msg.rs

+// run-fail
+// error-pattern:panicked at 'assertion failed: `(left != right)`
+// error-pattern: left: `2`
+// error-pattern:right: `2`: 1 + 1 definitely should not be 2'
+// ignore-emscripten no processes
+
+fn main() {
+    assert_ne!(1 + 1, 2, "1 + 1 definitely should not be 2");
+}