Replace some std::vectors that showed up in heap profiling with

Replace some std::vectors that showed up in heap profiling with
SmallVectors. Change the signature of TargetLowering::LowerArguments
to avoid returning a vector by value, and update the two targets
which still use this directly, Sparc and IA64, accordingly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52917 91177308-0d34-0410-b5e6-96231b3b80d8