Some macros are not well formatted

[rleungx]

There are some macros which are not well formatted in std, such as writeln.

macro_rules! writeln {
    ( $ dst : expr ) => { ... };
    (
$ dst : expr , $ fmt : expr ) => { ... };
    (
$ dst : expr , $ fmt : expr , $ ( $ arg : tt ) * ) => { ... };
}

Another example is unreachable.

macro_rules! unreachable {
    (  ) => { ... };
    (
$ msg : expr ) => { ... };
    (
$ fmt : expr , $ ( $ arg : tt ) * ) => { ... };
}

[sinkuu]

If they are ones reexported from libcore, this is #26560.

[pietroalbini]

Duplicate of #26560
Thanks for reporting this!