Use target-specific flags for building AArch64 non-runnable tests. Reviewed By: yota9 Differential Revision: https://reviews.llvm.org/D122520
Enable peephole optimizations for aarch64. Also small code refactoring - add PeepholeOpts under Peepholes class. Vladislav Khmelevsky, Advanced Software Technology Lab, Huawei Differential Revision: https://reviews.llvm.org/D118732