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

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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@155856 91177308-0d34-0410-b5e6-96231b3b80d8