CloneFunction: Clone all attributes, including the CC

Summary:
Tested with a unit test because we don't appear to have any transforms
that use this other than ASan, I think.

Fixes PR17935.

Reviewers: nicholas

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D3194

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204866 91177308-0d34-0410-b5e6-96231b3b80d8