Allow win_sdk build with USE_CCACHE=1

This patch allows the Window sdk build (lunch sdk-eng; make win_sdk)
to work properly when USE_CCACHE is defined in the environment.

There is no Windows ccache prebuilt, but since we're cross-compiling
from Linux, detect it and use the linux prebuilt binary instead.

Note: Depends on https://review.source.android.com//#change,21755
      for a complete solution to the problem.

Change-Id: I0b1b59efae86ee7114225258c9ecf9f257913347