Fix the issue of mangling of local anonymous unions (Itanium C++ ABI):
A discriminator is used for the first occurrence of a name.
inline int f1 () {
  static union {
    int a;
    long int b;
  };

  static union {
    int c;
    double d;
  };

  return a+c;
}
The name of the second union is mangled as _ZZ2f1vE1c_0 instead of _ZZ2f1vE1c.

Differential Revision: http://reviews.llvm.org/D6295