Builtin atomics fixes

[adayton1]

Summary

• This PR is a bugfix
• It does the following:
  • Modifies builtin atomics to use atomic loads to guarantee correctness
  • Fixes the call to the short-circuiting test by passing the original type rather than the value reinterpreted as unsigned or unsigned long
  • Refactors the atomic CAS in a loop operations for more code reuse (as well as a simpler implementation)
  • Provide a slightly faster implementation when there is no option for short-circuiting