Building ruby packages fails as a non root user

[Bernd Ernesti <netbsd%lists.veego.de@localhost>]

See pkg/39333 and e.g. for devel/ruby-debug-base, but no limited to it.
I have stopped countting the packages which fails the same way.

===> Building for ruby18-ruby-debug-base-0.10.1
(in /pkgsrc/devel/ruby-debug-base/work.i386/ruby-debug-base-0.10.1)
  Successfully built RubyGem
  Name: ruby-debug-base
  Version: 0.10.1
  File: ruby-debug-base-0.10.1.gem
=> Installing gem into installation root
Building native extensions.  This could take a while...
ERROR:  Error installing 
/pkgsrc/devel/ruby-debug-base/work.i386/ruby-debug-base-0.10.1/ruby-debug-base-0.10.1.gem:
        ERROR: Failed to build gem native extension.

/usr/pkg/bin/ruby18 extconf.rb install --no-update-sources --install-dir 
/usr/pkg/lib/ruby/gems/1.8 --install-root 
/pkgsrc/devel/ruby-debug-base/work.i386/.inst --local 
/pkgsrc/devel/ruby-debug-base/work.i386/ruby-debug-base-0.10.1/ruby-debug-base-0.10.1.gem
 -- --build-args
creating Makefile

make
cc -I. -I/usr/pkg/lib/ruby/1.8/i386-netbsdelf 
-I/usr/pkg/lib/ruby/1.8/i386-netbsdelf -I. -I/usr/include   -fPIC -O2 -pthread 
-I/usr/include  -fPIC -pipe  -c breakpoint.c
cc -I. -I/usr/pkg/lib/ruby/1.8/i386-netbsdelf 
-I/usr/pkg/lib/ruby/1.8/i386-netbsdelf -I. -I/usr/include   -fPIC -O2 -pthread 
-I/usr/include  -fPIC -pipe  -c ruby_debug.c
cc -shared -o ruby_debug.so breakpoint.o ruby_debug.o -L. -L/usr/pkg/lib 
-Wl,-R/usr/pkg/lib -L. -pthread -L/usr/lib -Wl,-R/usr/lib -Wl,-R/usr/pkg/lib 
-Wl,-export-dynamic    -Wl,-R -Wl,/usr/pkg/lib -L/usr/pkg/lib -lruby18  
-lpthread -lcrypt -lm   -lc

make install
/usr/bin/install -c -o root -g wheel -m 0755 ruby_debug.so 
/pkgsrc/devel/ruby-debug-base/work.i386/.inst/usr/pkg/lib/ruby/gems/1.8/gems/ruby-debug-base-0.10.1/lib
install: 
/pkgsrc/devel/ruby-debug-base/work.i386/.inst/usr/pkg/lib/ruby/gems/1.8/gems/ruby-debug-base-0.10.1/lib/ruby_debug.so:
 chown/chgrp: Operation not permitted
*** Error code 1

Stop.