HANG: linux.signal_race test hangs (and fails) on AArch64

The linux.signal_race test currently hangs during the busy wait on AArch64 and was disabled for AArch64 in PR #4453. The timing of the hang is non-deterministic (hangs at a different iteration every time) since the test tries to expose a race condition. Related issues: #2043 (closed), #4271 (closed).