When going through references to check if the function returns the address

of a local variable, make sure we don't infinitely recurse when the
reference binds to itself.

e.g:

int* func() {
    int& i = i;    // assign non-exist variable to a reference which has same name.
    return &i;    // return pointer
}

rdar://11345441

llvm-svn: 155856