[oe] Using native package build tree when building target package

[Ben Gamari]

Today I've been looking at the icu package, which is quite out-of-date
in the repository. Unfortunately, it seems that the latest version (4.6)
requires that the absolute path to a source tree built for the host be
passed to configure.

Does anyone have any clever ideas concerning how this might be
accomplished? Does this mean that we'll need to merge the icu and
icu-native recipes? My bitbake-fu is pretty weak, so I'd appreciate any
help. Thanks!

- Ben