Unprivileged build can't build custom kernels

["John D. Baker" <jdbaker%consolidated.net@localhost>]

The recent changes to build "netbsd-${CONF}.debug" seems not to work
for unprivileged builds when building custom kernels as it wants to
install the file owned by "root":

[...]
#      link  DAVID/netbsd
/r0/build/current/tools/amd64/bin/sparc--netbsdelf-ld -Map netbsd.map --cref -n -T netbsd.ldscript -Ttext F0004000 -e start -X -X -o netbsd ${SYSTEM_OBJ:[@]:Nswapnetbsd.o} ${EXTRA_OBJ} vers.o swapnetbsd.o
NetBSD 9.99.93 (DAVID) #376: Fri Dec 31 02:44:31 CST 2021
   text    data     bss     dec     hex filename
4808082  118584  147752 5074418  4d6df2 netbsd
+ mv -f netbsd netbsd.gdb
+ /r0/build/current/tools/amd64/bin/sparc--netbsdelf-objcopy --only-keep-debug netbsd.gdb netbsd-DAVID.debug
+ /r0/build/current/tools/amd64/bin/sparc--netbsdelf-objcopy --strip-debug -p -R .gnu_debuglink --add-gnu-debuglink=netbsd-DAVID.debug netbsd.gdb netbsd
+ chmod 755 netbsd netbsd.gdb netbsd-DAVID.debug
--- /r0/build/current/DEST/sparc/usr/libdata/debug/netbsd-DAVID.debug ---
#   install  /r0/build/current/DEST/sparc/usr/libdata/debug/netbsd-DAVID.debug
/r0/build/current/tools/amd64/bin/sparc--netbsdelf-install  -c -p -r -o root -g bin -m 444 netbsd-DAVID.debug /r0/build/current/DEST/sparc/usr/libdata/debug/netbsd-DAVID.debug
sparc--netbsdelf-install: /r0/build/current/DEST/sparc/usr/libdata/debug/netbsd-DAVID.debug.inst.fO9ANt: chown/chgrp: Operation not permitted

*** Failed target: /r0/build/current/DEST/sparc/usr/libdata/debug/netbsd-DAVID.debug
*** Failed commands:
        ${_MKTARGET_INSTALL}
        => @echo '#  ' "install " /r0/build/current/DEST/sparc/usr/libdata/debug/netbsd-DAVID.debug
        ${INSTALL_FILE} -o root -g bin -m 444 ${.ALLSRC} ${.TARGET}
        => /r0/build/current/tools/amd64/bin/sparc--netbsdelf-install  -c -p -r -o root -g bin -m 444 netbsd-DAVID.debug /r0/build/current/DEST/sparc/usr/libdata/debug/netbsd-DAVID.debug
*** [/r0/build/current/DEST/sparc/usr/libdata/debug/netbsd-DAVID.debug] Error code 1

nbmake: stopped in /r0/build/current/obj/sparc/sys/arch/sparc/compile/DAVID
1 error

nbmake: stopped in /r0/build/current/obj/sparc/sys/arch/sparc/compile/DAVID

ERROR: Failed to make debuginstall in "/r0/build/current/obj/sparc/sys/arch/sparc/compile/DAVID"
*** BUILD ABORTED ***


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