misc/53561: Build log contains gmake debug output

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

>Number:         53561
>Category:       misc
>Synopsis:       Build log contains gmake debug output
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    misc-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Aug 30 09:05:00 +0000 2018
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date >= 2016.04.03.06.13.28
>Organization:

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

On August 16, the i386 testbed sent out a build failure notification
which failed to include the compiler error messages, probably because
the heuristic for locating them was confused by several thousand lines
of GNU Make debug output in the log output from build.sh.  Some of it
ended up in the report:

        Still updating file `symtab.o'.
        Considering target file `traditional.o'.
        File `traditional.o' was considered already.
       Finished prerequisites of target file `libcpp.a'.
      The prerequisites of `libcpp.a' are being made.
     Finished prerequisites of target file `all'.
    The prerequisites of `all' are being made.
    Live child 0x7f7ff7b2a480 (init.o) PID 17958 
    Live child 0x7f7ff7b2a660 (symtab.o) PID 18497 
    Live child 0x7f7ff7b2a570 (macro.o) PID 14922 
    Live child 0x7f7ff7b2a4d0 (lex.o) PID 3561 
    Live child 0x7f7ff7b2a3e0 (files.o) PID 13987 
    Live child 0x7f7ff7b2a390 (expr.o) PID 9834 
    Live child 0x7f7ff7b2a2a0 (directives.o) PID 2536 
    Live child 0x7f7ff7b2a200 (charset.o) PID 2228 

IMO, this does not belong in the build log and should be suppressed.

I'm having trouble figuring out exactly where it is is printed, but
bisection shows that it appeared on source date 2016.04.03.06.13.28
with mrg's commit of src/share/mk/bsd.own.mk 1.917, which switched
amd64 and i386 to GCC 5.3.

>How-To-Repeat:

>Fix: