Disallow lifetime followed immediately by single quote

[dtolnay]

This is not lexed as two consecutive lifetime tokens in Rust.

macro_rules! m {
    ($($tt:tt)*) => {};
}

m!('aa'aa);

error: character literal may only contain one codepoint
 --> src/main.rs:5:4
  |
5 | m!('aa'aa);
  |    ^^^^
  |
help: if you meant to write a `str` literal, use double quotes
  |
5 | m!("aa"aa);
  |    ^^^^