[Bug libstdc++/59167] New: Add a specialization for std::hash<__gnu_debug::string>

[bmerry at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59167

            Bug ID: 59167
           Summary: Add a specialization for
                    std::hash<__gnu_debug::string>
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bmerry at gmail dot com

I have code for which I am explicitly selecting debug containers from the
__gnu_debug namespace (I'm not using -D_GLIBCXX_DEBUG since it breaks the ABI
with Boost and I don't want to require people to rebuild Boost to use a debug
build of my code).

This mostly works, but when I try to use an unordered_map with
__gnu_debug::string as the key type I get errors because std::hash hasn't been
specialized for it. I can write my own specialization, but it would be nice if
the library just provided it.

Obviously the other variants (wstring, u16string, u32string should be handled
too).