Instead, define explicit specializations for the basic types listed in
the SGI documentation. This solves two problems:
1) Helps avoid silent ODR violations caused by the absence of a
user-supplied __gnu_cxx::hash specialization in cases where a std::hash
specialization exists (e.g. for std::string).
2) __gnu_cxx::hash semantics are slightly different to those of
std::hash (for example, the former may dereference a pointer argument)
so it is inappropriate for __gnu_cxx::hash to receive std::hash
specializations by default.
Differential Revision: http://llvm-reviews.chandlerc.com/D2747
llvm-svn: 203070
Peter Collingbourne