misc/52997: Build logs from successful builds contain "fatal error"

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

>Number:         52997
>Category:       misc
>Synopsis:       Build logs from successful builds contain "fatal error"
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    misc-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Feb 09 21:15:00 +0000 2018
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current,source date 2018.02.09.17.14.26
>Organization:

>Environment:
System: NetBSD
Architecture: i386
Machine: i386
>Description:

When searching for the compiler error message in the log output from a
failed build, I found several error messages like the following:

  /tmp/bracket/build/2018.02.09.17.14.26-i386/src/external/cddl/osnet/dist/uts/common/sys/dtrace.h:55:24: fatal error: sys/modctl.h: No such file or directory
  compilation terminated.

However, this turned out not to be the cause of the build failure -
messages like the above also occur in every successful build log.
I don't know if the errors being reported are causing actual harm or
not, but regardless of that, they are confusing and make it harder to
find other errors that actually cause the build to fail.

The amd64 and evbarm-earmv7hf ports are also affected.

>How-To-Repeat:

Build NetBSD-current successfully.  Grep the build log for "fatal error".

>Fix: