Add a bunch of noexcepts to char_traits and string_view.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@276955 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/string_view b/include/string_view
index 08fcfd6..67fc606 100644
--- a/include/string_view
+++ b/include/string_view
@@ -356,7 +356,7 @@
 	}
 
 	_LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-	int compare(const _CharT* __s) const
+	int compare(const _CharT* __s) const _NOEXCEPT
 	{
 		return compare(basic_string_view(__s));
 	}