device targets.

The new recommendation for libffi usage is: Libffi is fine to use as a
means of bootstrapping your device build for a new architecture, but
you probably want to replace it with custom code before you ship. As
for a host build, if you need it (which isn't actually that likely),
you should use the libffi that comes with your platform or build it as
a normal library (e.g., download it and then "./configure; make
install").

Change-Id: I710daa136a2cacc4f95cdf6b5fd60a3d3c072df5

support darwin-x86.

The host-side build rules are protected by WITH_HOST_DALVIK, so as to
prevent it from building under normal circumstances. This change also
removes make target that runs all the tests, replacing it with a
bona fide shell script which now works for host builds (whereas the
old make target only worked for simulator builds).