Helgrind thread error detector test and analysis

[ming]

Helgrind is a thread detector tools which is useful to inform us about possible data races and violation of lock ordering. Undoubtedly, it will be a useful tool to test scenarios such as registration, audio/video calls, ICE, and so on.

Ideally, we should try to achieve as fewest warnings as possible, or if that's not possible, for issues which we have thoroughly analysed and identified as safe, create a suppression file (with the help of Helgrind's gen-suppression option), which can be used for future testing.

For known issues so far, please refer to ​this wiki

Note that Helgrind test will be done primarily on Linux since its Mac support, for now, is still quite limited.
Update (Jan 2020): the latest version, valgrind 3.15 supports MacOS, but only an older version 10.13 (while the latest is now 10.15. However when tested on 10.13, the memcheck stalled:

UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option

while Helgrind will assert:

Helgrind: hg_main.c:4559 (void instrument_mem_access(IRSB *, IRExpr *, Int, Bool, Bool, Int, Int, Int, IRExpr *)): Assertion 'szB > 8 && szB <= 512' failed.