checkflist i386/libstdcxx.so.1 libstdcxx.so.1.0 missing from DESTDIR?

[David Shao <davshao%gmail.com@localhost>]

On NetBSD 6.99.10 (GENERIC) amd64, cleaning /usr/obj and /usr/tools
(probably unrelated, /etc/mk.conf has lines
COPTS+=-g
MKDEBUG=yes
)
and performing

./build.sh -O ../obj -T ../tools -U distribution

results in a build error:

======  2 missing files in DESTDIR  ========
Files in flist but missing from DESTDIR.
File wasn't installed ?
------------------------------------------
./usr/lib/i386/libstdcxx.so.1
./usr/lib/i386/libstdcxx.so.1.0
========  end of 2 missing files  ==========


*** Failed target:  checkflist
*** Failed command: cd /usr/src/distrib/sets &&
DESTDIR=/usr/src/../obj/destdir.amd64 MACHINE=amd64
MACHINE_ARCH=x86_64 AWK=/usr/src/../tools/bin/nbawk
CKSUM=/usr/src/../tools/bin/nbcksum DB=/usr/src/../tools/bin/nbdb
HOST_SH=/bin/sh MAKE=/usr/src/../tools/bin/nbmake
MKTEMP=/usr/src/../tools/bin/nbmktemp
MTREE=/usr/src/../tools/bin/nbmtree PAX=/usr/src/../tools/bin/nbpax
COMPRESS_PROGRAM=gzip PKG_CREATE=/usr/src/../tools/bin/nbpkg_create
SED=/usr/src/../tools/bin/nbsed TSORT=/usr/src/../tools/bin/nbtsort\
-q /bin/sh /usr/src/distrib/sets/checkflist -L base -M
/usr/src/../obj/destdir.amd64/METALOG.sanitised
*** Error code 1