Rollup merge of #21924 - steveklabnik:fix_try_docs, r=huonw

 This is now a Result, not an Option.

diff --combined src/libstd/rt/unwind.rs
index b37996fa9d9de0163fc434b786f4d17676d37b88,cb2172d1dfc25746e5be471727e6bea7dea09454..e064663b9e76f3931ed28f1e8ee69b86cb163bb8
--- 1/src/libstd/rt/unwind.rs
--- 2/src/libstd/rt/unwind.rs
+++ b/src/libstd/rt/unwind.rs
@@@ -98,8 -98,8 +98,8 @@@ thread_local! { static PANICKING: Cell<
  
  /// Invoke a closure, capturing the cause of panic if one occurs.
  ///
- /// This function will return `None` if the closure did not panic, and will
- /// return `Some(cause)` if the closure panics. The `cause` returned is the
+ /// This function will return `Ok(())` if the closure did not panic, and will
+ /// return `Err(cause)` if the closure panics. The `cause` returned is the
  /// object with which panic was originally invoked.
  ///
  /// This function also is unsafe for a variety of reasons:
@@@ -390,10 -390,13 +390,10 @@@ pub mod eabi 
      use libc::{c_void, c_int};
  
      #[repr(C)]
 -    #[allow(missing_copy_implementations)]
      pub struct EXCEPTION_RECORD;
      #[repr(C)]
 -    #[allow(missing_copy_implementations)]
      pub struct CONTEXT;
      #[repr(C)]
 -    #[allow(missing_copy_implementations)]
      pub struct DISPATCHER_CONTEXT;
  
      #[repr(C)]