Sync libiberty with gcc and add Rust demangling support to cxxfilt.

[Nick Clifton]

Hi Mark,

> OK to push these patches?
> 
>  [PATCH 01/10] PR c++/71696 testcase.
>  [PATCH 02/10] libiberty: Fix memory leak in ada_demangle when symbol
>  [PATCH 03/10] Implement P0136R1, Rewording inheriting constructors.
>  [PATCH 04/10] libiberty: Fix -Wimplicit-fallthrough warnings.
>  [PATCH 05/10] Implement P0012R1, Make exception specifications part
>  [PATCH 06/10] libiberty: Add -Wshadow=local to warning flags (if
>  [PATCH 07/10] libiberty: Fix some demangler crashes caused by reading
>  [PATCH 08/10] libiberty: demangler crash with missing :? or fold
>  [PATCH 09/10] libiberty: Add Rust symbol demangling.
>  [PATCH 10/10] cxxfilt: Recognize rust_demangling.

Yes - please apply (the whole series).

Cheers
  Nick