Modernize macro_rules! invocations

macro_rules! is like an item that defines a macro.  Other items don't have a
trailing semicolon, or use a paren-delimited body.

If there's an argument for matching the invocation syntax, e.g. parentheses for
an expr macro, then I think that applies more strongly to the *inner*
delimiters on the LHS, wrapping the individual argument patterns.

src/test/run-pass/syntax-extension-source-utils.rs

@@ -21,7 +21,7 @@ pub mod m1 {
     }
 }
 
-macro_rules! indirect_line( () => ( line!() ) );
+macro_rules! indirect_line { () => ( line!() ) }
 
 pub fn main() {
     assert_eq!(line!(), 27);