Motivated by the work on the llvm.noalias intrinsic, teach BasicAA to look
through returned-argument functions when answering queries. This is essential
so that we don't loose all other AA information when supplementing with
llvm.noalias.
Differential Revision: http://reviews.llvm.org/D9383
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275035 91177308-0d34-0410-b5e6-96231b3b80d8
