The AArch64 target itself is similar to the X86 target added in https://reviews.llvm.org/rL348903.
The llvm-exegesis AArch64 bits are similar to the X86 bits in http://reviews.llvm.org/rL350184.
The llvm-exegesis unittests AArch64 bits are similar to the X86 bits in https://reviews.llvm.org/rL350413
llvm/unittests/Target/AArch64 doesn't have an equivalent since the X86 Target only has lit tests, no unittests.