Provide hashers for string_view only if they are using the default char_traits. Seen on SO: test/std/strings/string.view/string.view.hash/char_type.hash.fail.cpp

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@364545 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed