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The first approach of building icu4j against the SDK and adding that
to the boot classpath won't work out too well. Besides being a bit
of a hack, there's no way to express that relationship for hostdex
builds.

We now compile icu4j sources along with core-libart. This is the most
direct way of expressing this relationship and allows us to include
exactly what we need.

Note that we exclude the locale SPIs, transliterators and charset code
by default.

Change-Id: Idd305e77480bc681ed5b47e740dfec20d3bc7b26