We have to use := instead of +=
We have to use := instead of +=

If we use +=, the right side may be deferred to evaluate,
if that target-specific variable is not defined yet.
That's a mistke.

Change-Id: I1635ee4791473f407866e010d612948c02cdebf6

xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build