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/attr.rs

@@ -29,7 +29,7 @@ use std::cell::{RefCell, Cell};
 use std::collections::BitvSet;
 use std::collections::HashSet;
 
-thread_local!(static USED_ATTRS: RefCell<BitvSet> = RefCell::new(BitvSet::new()))
+thread_local! { static USED_ATTRS: RefCell<BitvSet> = RefCell::new(BitvSet::new()) }
 
 pub fn mark_used(attr: &Attribute) {
     let AttrId(id) = attr.node.id;
@@ -169,7 +169,7 @@ pub fn mk_word_item(name: InternedString) -> P<MetaItem> {
     P(dummy_spanned(MetaWord(name)))
 }
 
-thread_local!(static NEXT_ATTR_ID: Cell<uint> = Cell::new(0))
+thread_local! { static NEXT_ATTR_ID: Cell<uint> = Cell::new(0) }
 
 pub fn mk_attr_id() -> AttrId {
     let id = NEXT_ATTR_ID.with(|slot| {