librustc: Always parse macro!()/macro![] as expressions if not

followed by a semicolon.

This allows code like `vec![1i, 2, 3].len();` to work.

This breaks code that uses macros as statements without putting
semicolons after them, such as:

    fn main() {
        ...
        assert!(a == b)
        assert!(c == d)
        println(...);
    }

It also breaks code that uses macros as items without semicolons:

    local_data_key!(foo)

    fn main() {
        println("hello world")
    }

Add semicolons to fix this code. Those two examples can be fixed as
follows:

    fn main() {
        ...
        assert!(a == b);
        assert!(c == d);
        println(...);
    }

    local_data_key!(foo);

    fn main() {
        println("hello world")
    }

RFC #378.

Closes #18635.

[breaking-change]

src/librustdoc/html/format.rs

@@ -779,7 +779,7 @@ The counts do not include methods or trait
 implementations that are visible only through a re-exported type.",
 stable, unstable, experimental, deprecated, unmarked,
 name=self.name));
-        try!(write!(f, "<table>"))
+        try!(write!(f, "<table>"));
         try!(fmt_inner(f, &mut context, self));
         write!(f, "</table>")
     }