port-amd64/54001: call_once2_32, call_once2_static test cases failing on amd64 since gcc7 import

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

>Number:         54001
>Category:       port-amd64
>Synopsis:       call_once2_32, call_once2_static test cases failing on amd64 since gcc7 import
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Feb 22 09:15:00 +0000 2019
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:

>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

The following test cases are consistently failing for me on real amd64
hardware since the import of GCC 7:

  usr.bin/c++/t_call_once2/call_once2_32
  usr.bin/c++/t_call_once2/call_once2_static

Recent log output is at:

  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2019/2019.02.21.14.56.23/test.html#usr.bin_c++_t_call_once2_call_once2_32
  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2019/2019.02.21.14.56.23/test.html#usr.bin_c++_t_call_once2_call_once2_static

They do not fail reliably under qemu, but one failures is recorded at:

  http://releng.netbsd.org/b5reports/amd64/2019/2019.02.20.19.42.14/test.html#usr.bin_c++_t_call_once2_call_once2_static

>How-To-Repeat:

>Fix: