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/libstd/sys/unix/mod.rs

@@ -23,7 +23,7 @@ use prelude::*;
 use io::{mod, IoResult, IoError};
 use sys_common::mkerr_libc;
 
-macro_rules! helper_init( (static $name:ident: Helper<$m:ty>) => (
+macro_rules! helper_init { (static $name:ident: Helper<$m:ty>) => (
     static $name: Helper<$m> = Helper {
         lock: ::sync::MUTEX_INIT,
         cond: ::sync::CONDVAR_INIT,
@@ -32,7 +32,7 @@ macro_rules! helper_init( (static $name:ident: Helper<$m:ty>) => (
         initialized: ::cell::UnsafeCell { value: false },
         shutdown: ::cell::UnsafeCell { value: false },
     };
-) )
+) }
 
 pub mod c;
 pub mod ext;