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/libsyntax/codemap.rs

@@ -329,7 +329,7 @@ impl FileMap {
         // the new charpos must be > the last one (or it's the first one).
         let mut lines = self.lines.borrow_mut();
         let line_len = lines.len();
-        assert!(line_len == 0 || ((*lines)[line_len - 1] < pos))
+        assert!(line_len == 0 || ((*lines)[line_len - 1] < pos));
         lines.push(pos);
     }