message: Gracefully fail if `use_std` is not used
  Use `compile_error!` macro to issue a meaningful compile error if the `use_std` feature is not enabled.
diff: @@ -521,6 +521,11 @@ another matching engine with fixed memory requirements.
  #![cfg_attr(test, deny(warnings))]
  #![cfg_attr(feature = "pattern", feature(pattern))]
  +
  +#[cfg(not(feature = "use_std"))]
  +compile_error!("`use_std` feature is currently required to build this crate");
  +
  +
  extern crate aho_corasick;
  extern crate memchr;
  extern crate thread_local;
  