toolchain/55770: Some tsan tests fail randomly on real hardware

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         55770
>Category:       toolchain
>Synopsis:       Some tsan tests fail randomly on real hardware
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Oct 31 12:45:00 +0000 2020
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:
>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

In addition to the tsan test cases failing in every run on real amd64
hardware as reported in PR 55760, others are failing randomly.

The following have failed in the last 40 runs on my bare metal testbed:

X--XX-XXXX--X----X-XX--X-XX---X-----XX-X   usr.bin/c++/t_tsan_data_race:data_race
---X-X-XX-X---X--XX-X----XX---X-XX--X---   usr.bin/c++/t_tsan_data_race:data_race_pic
XXXXX-XX-XX-X-X-X---------------------X-   usr.bin/c++/t_tsan_data_race:data_race_pie
-----X----------------------------------   usr.bin/c++/t_tsan_vptr_race:vptr_race
-------------------------------------X-X   usr.bin/c++/t_tsan_vptr_race:vptr_race_pie
-----------------X----X------X------X---   usr.bin/cc/t_tsan_data_race:data_race
------------X---X-X---------------------   usr.bin/cc/t_tsan_data_race:data_race_pic
--X-------------------------------------   usr.bin/cc/t_tsan_data_race:data_race_pie

In the table to the left, each successful run is represented by "-",
and each failure by "X", with CVS time increasing towards the right.
Logs from the most recent run can be found at:

  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/commits-2020.10.html#2020.10.30.22.03.35

>How-To-Repeat:

>Fix: