More of P0600 - '[[nodiscard]] in the Library' mark empty() as nodiscard in string, string_view, and the free function std::empty(). Removed tabs from <string_view>, which is why the diff is so big.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@318328 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed