Set flag when using sdk tools in place

New version of build/ execute the tools from prebuilts/sdk/tools in
place, old versions copy them to $(HOST_OUT_EXECUTABLES).  build/ and
prebuilts/sdk often use mixed versions, set a flag that
prebuilts/sdk/tools/Android.mk can use to determine when it is using an
old build/ directory.

Change-Id: Iad2f96c35203fd3b0976946d229bfa8ab4acb150
1 file changed