[PATCH] Fix to PR15537 - assertion failure when comparing atomic unsigned int to int.

[Doug Gregor]

  I'm confused as to why we're not just extending the checks here:

    if (LHS.get()->getType()->isArithmeticType() &&
        RHS.get()->getType()->isArithmeticType()) {

  to allow arithmetic or _Atomic of arithmetic?

http://llvm-reviews.chandlerc.com/D599