Support #[allow] etc logic on a per macro level

This commit extends the current unused macro linter
to support directives like #[allow(unused_macros)]
or #[deny(unused_macros)] directly next to the macro
definition, or in one of the modules the macro is
inside. Before, we only supported such directives
at a per crate level, due to the crate's NodeId
being passed to session.add_lint.

We also had to implement handling of the macro's
NodeId in the lint visitor.

src/libsyntax/ext/base.rs

@@ -535,7 +535,7 @@ pub enum SyntaxExtension {
     ///
     /// The `bool` dictates whether the contents of the macro can
     /// directly use `#[unstable]` things (true == yes).
-    NormalTT(Box<TTMacroExpander>, Option<Span>, bool),
+    NormalTT(Box<TTMacroExpander>, Option<(ast::NodeId, Span)>, bool),
 
     /// A function-like syntax extension that has an extra ident before
     /// the block.