Libcore: Allow "os.arch" system property to be changed

In a native bridge environment, it is necessary to change the "os.arch"
system property to reflect the emulated architecture.

Change-Id: I0b93da93251c6b4638de786bf98cf99df07c3fc2
Signed-off-by: jgu21 <jinghui.gu@intel.com>
Merge "Libcore: Allow "os.arch" system property to be changed"