message: Clarify localeconv mutability
diff: @@ -32,7 +32,8 @@ pub struct lconv {
  }
  unsafe impl Sync for lconv {}
  -//TODO: thread local?
  +// Mutable because POSIX demands a mutable pointer, even though it warns
  +// against mutating it
  static mut CURRENT_LOCALE: lconv = lconv {
  currency_symbol: EMPTY_PTR,
  decimal_point: ".\0" as *const _ as *const c_char,
  