First parts of enabling a host Dalvik build.

First parts of enabling a host Dalvik build.

Most of this is just factoring out common make defs to include both on
the host and device side, though there is a little bit of code change
to be slightly POSIX friendlier and to avoid unnecessary sanity checks
when compiling without an asm version of the interpreter.

This patch should cause no difference in build results, except if you
turn on the newly-defined WITH_HOST_DALVIK build flag. If you do turn
it on, at this point you should probably expect the build to fail due
to insufficient dependencies, which I of course expect to address in
upcoming patches.