add a new helper method. It is unclear to me why this doesn't work, but GCC

add a new helper method.  It is unclear to me why this doesn't work, but GCC
won't match it:

  template<std::size_t StrLen>
  bool isName(const char Str[StrLen]) const {
    return getLength() == StrLen-1 && !memcmp(getName(), Str, StrLen-1);
  }

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59605 91177308-0d34-0410-b5e6-96231b3b80d8