client.drwrap-test-detach fails 28/100 times on aarch64: hang

Split from #1578 Xref #4474

Other issues revealed by this test: Xref #4616: timeout on Windows Xref #4593: failed several times on GA CI on 32-bit x86: mysterious crashes Xref #4219: Translation problems in clean call mangling causing post-detach crashes

See https://github.com/DynamoRIO/dynamorio/pull/4467#issuecomment-705049234 where it fails 28/100 times on Jenkins.

On tx1 I saw a weird failure where the output seems to match:

derek@tx1:~/dr/build$ ctest --repeat-until-fail 100 -V -R drwrap-test-detach

209: Test command: /home/derek/dr/build/bin64/runstats "-s" "90" "-killpg" "-silent" "-env" "LD_LIBRARY_PATH" "/home/derek/dr/build/lib64/debug:/home/derek/dr/build/ext/lib64/debug:" "-env" "DYNAMORIO_OPTIONS" "-stderr_mask 0xC -dumpcore_mask 0 -code_api" "/home/derek/dr/build/suite/tests/bin/client.drwrap-test-detach"
209: Test timeout computed to be: 1500
209: in dr_client_main
209: client done
209: app done
    Test #209: code_api|client.drwrap-test-detach ...   Passed    0.63 sec
    Start 209: code_api|client.drwrap-test-detach

209: Test command: /home/derek/dr/build/bin64/runstats "-s" "90" "-killpg" "-silent" "-env" "LD_LIBRARY_PATH" "/home/derek/dr/build/lib64/debug:/home/derek/dr/build/ext/lib64/debug:" "-env" "DYNAMORIO_OPTIONS" "-stderr_mask 0xC -dumpcore_mask 0 -code_api" "/home/derek/dr/build/suite/tests/bin/client.drwrap-test-detach"
209: Test timeout computed to be: 1500
209: in dr_client_main
209: client done
209: app done
    Test #209: code_api|client.drwrap-test-detach ...***Failed  Required regular expression not found.Regex=[^in dr_client_main
client done
app done
$
]  0.63 sec

Instead running in a loop we see a hang on the 3rd invocation:

derek@tx1:~/dr/build$ for ((i=0; i<100; i++)); do echo -e "\n============\n$i\n"; LD_LIBRARY_PATH=lib64/debug DYNAMORIO_OPTIONS="-stderr_mask 0xf -dumpcore_mask 0 -code_api" suite/tests/bin/client.drwrap-test-detach; done > OUT 2>&1

A loop with the harness to time out:

derek@tx1:~/dr/build$ for ((i=0; i<100; i++)); do echo -e "\n============\n$i\n"; ctest -V -R drwrap-test-detach; done > OUT 2>&1

That is in progress; will update when done. So far, seeing a lot of hangs. Has no reproduced the weird failure above.