Returns true when arg contains a byte cmd.exe would reinterpret while
re-tokenizing the command line of a .bat/.cmd invocation: " breaks
out of libuv’s MSVCRT-style quoting, % expands environment variables
even inside quotes, and the rest are command separators / redirection /
escape characters in unquoted positions. None of these can be escaped for
cmd.exe, so callers must reject the spawn instead.