Fix flaky tests on AArch64

[fhahn]

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Currently, the following tests are flaky on some AArch64 hardware

 code_api|pthreads.pthreads_fork_FLAKY
 code_api|linux.sigsuspend
 code_api|pthreads.pthreads_exit
 code_api|security-common.TestMemProtChg_FLAKY
 code_api|pthreads.ptsig_FLAKY
 code_api|linux.fib-conflict
 code_api|linux.fib-conflict-early

[egrimley]

I have the impression that code_api|security-common.TestMemProtChg_FLAKY isn't "flaky": it seems to pass or fail consistently depending on the system.

[johnfxgalea]

Ref: security-common.TestMemProtChg_FLAKY failed: http://139.178.83.194:8080/job/DynamoRIO-AArch64-Precommit/765/

[AssadHashmi]

The following tests fail on the new Jenkins CI host, an Ampere Altra:

code_api|tool.drcachesim.phys #4922 code_api|tool.drcacheoff.rseq #4924 code_api|api.rseq #4923 code_api|tool.drcachesim.threads #4928 code_api|tool.drcachesim.TLB-threads #4928

[joshua-warburton]

Additionally, drcachesim.coherence times out on many different aarch64 hosts. It intermittently times out in the precommit of this repo and seems to always time out on our aws-based ci.

[derekbruening]

The drcachesim.coherence test, like #4928 and #4954, only times out in release build

[derekbruening]

drcachesim.coherence is fixed by the same fix for #4928: PR #5375