port-amd64/54000: FP tests failing on amd64 since gcc7 import

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

>Number:         54000
>Category:       port-amd64
>Synopsis:       FP tests failing on amd64 since gcc7 import
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Feb 22 08:45:00 +0000 2019
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:

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

The following tests are failing on amd64 since the import of gcc 7:

  lib/libc/gen/t_fpsetround/fpsetround_basic
  lib/libm/t_fe_round/fe_nearbyint
  lib/libm/t_fe_round/fe_round

They fail both under qemu and on real hardware, but not on i386.
For recent log output, see:

  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2019/2019.02.21.14.56.23/test.html#lib_libc_gen_t_fpsetround_fpsetround_basic
  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2019/2019.02.21.14.56.23/test.html#lib_libm_t_fe_round_fe_nearbyint
  http://www.gson.org/netbsd/bugs/build/amd64-baremetal/2019/2019.02.21.14.56.23/test.html#lib_libm_t_fe_round_fe_round
  http://releng.netbsd.org/b5reports/amd64/2019/2019.02.20.19.42.14/test.html#lib_libc_gen_t_fpsetround_fpsetround_basic
  (etc)

>How-To-Repeat:

Run the ATF tests on amd64.

>Fix: