toolchain/49276: amd64 MKDEBUG builds randomly fail installing compat libraries

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

>Number:         49276
>Category:       toolchain
>Synopsis:       amd64 MKDEBUG builds randomly fail installing compat libraries
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Oct 12 15:50:00 +0000 2014
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source dates around 2014.10.10.17.09.18
>Organization:
>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

I'm trying to do debug builds (MKDEBUG=YES) of NetBSD-current/amd64
on a NetBSD/amd64 6.1.4 machine.  Since the machine has four cores,
I'm also passing build.sh the option "-j 4".

About half of these builds fail, with errors like this:

  --- install-compat ---
  --- /tmp/bracket/build/2014.10.10.17.09.18-amd64-debug/destdir/usr/lib/i386/libpcap.so.5.0 ---
  x86_64--netbsd-install: libpcap.so.5.0: stat: No such file or directory
  *** [/tmp/bracket/build/2014.10.10.17.09.18-amd64-debug/destdir/usr/lib/i386/libpcap.so.5.0] Error code 1
  nbmake[8]: stopped in /tmp/bracket/build/2014.10.10.17.09.18-amd64-debug/src/external/bsd/libpcap/lib

Or this:

  --- install-libbind9 ---
  --- /tmp/bracket/build/2014.10.11.08.22.34-amd64-debug/destdir/usr/lib/i386/libbind9.so.8.0 ---
  x86_64--netbsd-install: libbind9.so.8.0: stat: No such file or directory
  --- install-libirs ---
  --- /tmp/bracket/build/2014.10.11.08.22.34-amd64-debug/destdir/usr/libdata/debug/usr/lib/i386/libirs.so.8.0.debug ---
  --- install-libbind9 ---
  *** [/tmp/bracket/build/2014.10.11.08.22.34-amd64-debug/destdir/usr/lib/i386/libbind9.so.8.0] Error code 1
  nbmake[9]: stopped in /tmp/bracket/build/2014.10.11.08.22.34-amd64-debug/src/external/bsd/bind/lib/libbind9

The exact library involved changes from run to run, but they're all in
/usr/lib/i386.  This looks like a parallel make race condition of some
sort, like the closed PR 44046 but specific to the i386 compat libraries.

>How-To-Repeat:

Do a few amd64 release builds using build.sh with the options
"-j 4 -V MKDEBUG=YES".  Watch about half of them fail.

>Fix: