HANG OSX hello, free, and asmtest

This happened in one OSX run for PR #2385 but on re-run did not reproduce:
```
2021-02-07T19:04:08.3180560Z xxxxxxxxxx 30s elapsed xxxxxxxxxxx
2021-02-07T19:04:08.3181630Z 2/13 Test #3: hello ............................***Timeout 120.21 sec
2021-02-07T19:04:08.3184080Z
2021-02-07T19:04:08.3184710Z test 11
2021-02-07T19:04:08.3185270Z Start 11: bitfield
2021-02-07T19:04:08.3185740Z
2021-02-07T19:04:08.3191460Z 11: Test command: /usr/local/Cellar/cmake/3.19.4/bin/cmake "-D" "cmd:STRING=/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/bin64/drmemory@-debug@-dr_debug@-dr@{DRMEMORY_CTEST_DR_DIR}/..@-batch@-dr_ops@-dumpcore_mask@-dr_ops@0@-callstack_style@0x27@-no_results_to_stderr@--@/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/tests/bitfield" "-D" "TOOL_DR_HEAPSTAT:BOOL=OFF" "-D" "outpat:STRING={DRMEMORY_CTEST_SRC_DIR}/bitfield.out" "-D" "respat:STRING={DRMEMORY_CTEST_SRC_DIR}/bitfield.res" "-D" "resmark:STRING=Details:" "-D" "nudge:STRING=/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/bin64/drmemory@-debug@-dr_debug@-dr@{DRMEMORY_CTEST_DR_DIR}/..@-batch" "-D" "VMKERNEL:BOOL=OFF" "-D" "X64:BOOL=ON" "-D" "ARM:BOOL=" "-D" "ANDROID:BOOL=" "-D" "ADB:FILEPATH=" "-D" "toolbindir:STRING={DRMEMORY_CTEST_DR_DIR}/../bin64" "-D" "DRMEMORY_CTEST_SRC_DIR:STRING=/Users/runner/work/drmemory/drmemory/tests" "-D" "DRMEMORY_CTEST_DR_DIR:STRING=/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/dynamorio/cmake" "-D" "CMAKE_SYSTEM_VERSION:STRING=19.6.0" "-D" "exit_code:STRING=0" "-D" "path_append:STRING=" "-D" "timeout:STRING=120" "-D" "postcmd:STRING=" "-P" "/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/tests/runtest.cmake"
2021-02-07T19:04:08.3195760Z 11: Test timeout computed to be: 120
2021-02-07T19:04:08.3196470Z 3/13 Test #6: free .............................***Timeout 120.43 sec
2021-02-07T19:04:08.3196990Z
2021-02-07T19:04:08.3197500Z test 14
2021-02-07T19:04:08.3198030Z Start 14: float
2021-02-07T19:04:08.3198470Z
2021-02-07T19:04:08.3204470Z 14: Test command: /usr/local/Cellar/cmake/3.19.4/bin/cmake "-D" "cmd:STRING=/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/bin64/drmemory@-debug@-dr_debug@-dr@{DRMEMORY_CTEST_DR_DIR}/..@-batch@-dr_ops@-dumpcore_mask@-dr_ops@0@-callstack_style@0x27@-no_results_to_stderr@--@/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/tests/float" "-D" "TOOL_DR_HEAPSTAT:BOOL=OFF" "-D" "outpat:STRING={DRMEMORY_CTEST_SRC_DIR}/float.out" "-D" "respat:STRING={DRMEMORY_CTEST_SRC_DIR}/float.res" "-D" "resmark:STRING=Details:" "-D" "nudge:STRING=/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/bin64/drmemory@-debug@-dr_debug@-dr@{DRMEMORY_CTEST_DR_DIR}/..@-batch" "-D" "VMKERNEL:BOOL=OFF" "-D" "X64:BOOL=ON" "-D" "ARM:BOOL=" "-D" "ANDROID:BOOL=" "-D" "ADB:FILEPATH=" "-D" "toolbindir:STRING={DRMEMORY_CTEST_DR_DIR}/../bin64" "-D" "DRMEMORY_CTEST_SRC_DIR:STRING=/Users/runner/work/drmemory/drmemory/tests" "-D" "DRMEMORY_CTEST_DR_DIR:STRING=/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/dynamorio/cmake" "-D" "CMAKE_SYSTEM_VERSION:STRING=19.6.0" "-D" "exit_code:STRING=0" "-D" "path_append:STRING=" "-D" "timeout:STRING=120" "-D" "postcmd:STRING=" "-P" "/Users/runner/work/drmemory/drmemory/build_drmemory-dbg-64/tests/runtest.cmake"
2021-02-07T19:04:08.3208830Z 14: Test timeout computed to be: 120
2021-02-07T19:04:08.3209570Z 4/13 Test #9: asmtest ..........................***Timeout 120.14 sec
```