[CodeGen] [CodeGen] Attach function attributes to functions created in

CGBlocks.cpp.

This commit fixes a bug in clang's code-gen where it creates the
following functions but doesn't attach function attributes to them:

__copy_helper_block_
__destroy_helper_block_
__Block_byref_object_copy_
__Block_byref_object_dispose_

rdar://problem/20828324

Differential Revision: http://reviews.llvm.org/D13525

llvm-svn: 249735