Back the optimization down from -O3 to -Os. I'm getting an unexplained...

Back the optimization down from -O3 to -Os.  I'm getting an unexplained crasher on -O3.  I've looked for a libc++abi bug and can't find one.  I'm suspecting clang optimizer bug.  But I don't have a good test case at the moment.  Deferring investigation on this for now as I will soon be developing more and smaller tests.

llvm-svn: 149414