Add a bunch of noexcepts to char_traits and string_view.

llvm-svn: 276955
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: aa849bc2f23432af3104b2c1524009312bcad223
2 files changed