Revert commit r186217 -- this is breaking bots:

  http://lab.llvm.org:8013/builders/clang-x86_64-darwin11-nobootstrap-RAincremental/builds/4328

Original commit log:
  Use the function attributes to pass along the stack protector buffer
  size.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186234 91177308-0d34-0410-b5e6-96231b3b80d8