[XRay][AArch64] Disable the unstable test XRay-aarch64-linux::patching-unpatching.cc

Summary:
The test `XRay-aarch64-linux::patching-unpatching.cc` sometimes passes, sometimes fails on buildbots.
This patch disables test `patching-unpatching.cc` for AArch64 targets.

Reviewers: rengolin, dberris

Subscribers: llvm-commits, iid_iunknown, aemerson

Differential Revision: https://reviews.llvm.org/D27528

llvm-svn: 288988