Expand core::panic!() to always include { .. }.

std::panic!() always expanded to a `{..}` block, but core::panic!() did
not. Because of this subtle difference, the issue-5500-1 test passed
for std::panic!(), but not for core::panic!().

This makes them behave the same, and extends that test to also check
core::panic!().

Author: m-ou-se

library/core/src/macros/mod.rs

@@ -7,15 +7,15 @@ macro_rules! panic {
     () => (
         $crate::panic!("explicit panic")
     );
-    ($msg:literal $(,)?) => (
+    ($msg:literal $(,)?) => ({
         $crate::panicking::panic($msg)
-    );
-    ($msg:expr $(,)?) => (
+    });
+    ($msg:expr $(,)?) => ({
         $crate::panicking::panic_str($msg)
-    );
-    ($fmt:expr, $($arg:tt)+) => (
+    });
+    ($fmt:expr, $($arg:tt)+) => ({
         $crate::panicking::panic_fmt($crate::format_args!($fmt, $($arg)+))
-    );
+    });
 }
 
 /// Asserts that two expressions are equal to each other (using [`PartialEq`]).

src/test/ui/issues/issue-5500-1.rs

@@ -11,5 +11,6 @@ struct TrieMapIterator<'a> {
 fn main() {
     let a = 5;
     let _iter = TrieMapIterator{node: &a};
-    _iter.node = &panic!()
+    _iter.node = &panic!();
+    _iter.node = &core::panic!()
 }