Make to_chars/from_chars work back to C++11. This means that we can use them to implement to_string as well. Reviewed as https://reviews.llvm.org/D59598.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@356585 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed