PR libstdc++/59529, 59530,59531 Various string_view bugs.

[Paolo Carlini]

Ed Smith-Rowland <3dw4rd@verizon.net> ha scritto:
>As committed:
>
>Same patch as discussed before all the holidays.
>
>Built and tested x86_64-linux.

Thanks. Please remember to also close the bugs.

Paolo.