[AArch64] Add test for function alignment for a optsize function (NFC).

Reviewers: dblaikie, t.p.northover, rengolin

Reviewed By: rengolin

Subscribers: aemerson, rengolin, javed.absar, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D35620

llvm-svn: 308852