Fix an issue of pseudo atomic instruction DAG schedule

- Add list of physical registers clobbered in pseudo atomic insts
  Physical registers are clobbered when pseudo atomic instructions are
  expanded. Add them in clobber list to prevent DAG scheduler to
  mis-schedule them after these insns are declared side-effect free.
- Add test case from Michael Kuperstein <michael.m.kuperstein@intel.com>

llvm-svn: 173200