Rename a helper template function to 'bytes' to avoid a C++17 STL conflict

MSVC 2015 includes the std::data() template function added to C++17. ADL
causes both cl.exe and clang-cl to prefer std::data over our static
helper here, and we get errors about converting int64_t* to StringRef.
Renaming it to bytes avoids the ambiguity.

llvm-svn: 237863