[stack protector] Refactor and clean-up test.  No functionality change.

Refactored stack-protector.ll to use new-style function attributes everywhere
and eliminated unnecessary attributes.

This cleanup is in preparation for an upcoming test change.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205996 91177308-0d34-0410-b5e6-96231b3b80d8