Fix for clang_Cursor_getSpellingNameRange()

Summary:
Fixes spelling name ranges for user-defined string literal operators.

Example:
  constexpr int operator""_toint(unsigned long long val)
  { return int(val); }

Before this patch the spelling name range on consisted of 'operator'.

After this patch: 'operator""_toint'.

Related to http://reviews.llvm.org/D5041, which fixes the function for
other cursor kinds.

Reviewers: akyrtzi, craigt, skalinichev, klimek, milianw, bkramer

Subscribers: cfe-commits

Tags: #clang-c

Differential Revision: https://reviews.llvm.org/D18462

llvm-svn: 290172