LWG#2156 loosened the requirements on unordered containers 'rehash' calls. Add tests to make sure we meet these requirements. Since we met the stricter ones, no code change needed to meet the looser ones.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@253223 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed