C++ PATCH for c++/58102 (constexpr and mutable)

[Paolo Carlini]

On 11/18/2014 02:35 PM, Jason Merrill wrote:
> We need to allow copy-list-initialization of constexpr variables with 
> mutable members, too.  The thing we need to avoid is not so much an 
> full-expression with mutable-containing type as assuming that a 
> mutable member of a variable hasn't changed since the variable was 
> initialized.
Thanks. You suggest a similar fix a while ago but I failed to pursue it, 
sorry.

Paolo.