ldconfig does not work for non-native arches. Create a new
build_image routine run_ldconfig that uses qemu user emulation
to run the board ldconfig on the board rootfs when the board and
SDK arches are different.
See: http://code.google.com/p/chromium/issues/detail?id=378377
Prior to calling run_ldconfig the board rootfs must have ldconfig
installed. To arrange this move the call of run_ldconfig to after
the base package install.
Fixes build_image errors like these when building for arm64:
/sbin/ldconfig: /lib64/libXXX is for unknown machine 183.
Signed-off-by: Geoff Levand <geoff@infradead.org>