cfg_attr_multi: Basic implementation

Does not implement the warning or a feature flag.

src/libsyntax/parse/parser.rs

@@ -678,7 +678,7 @@ impl<'a> Parser<'a> {
     /// Expect next token to be edible or inedible token.  If edible,
     /// then consume it; if inedible, then return without consuming
     /// anything.  Signal a fatal error if next token is unexpected.
-    fn expect_one_of(&mut self,
+    pub fn expect_one_of(&mut self,
                          edible: &[token::Token],
                          inedible: &[token::Token]) -> PResult<'a,  ()>{
         fn tokens_to_string(tokens: &[TokenType]) -> String {