product_config: Set CM_BUILD priority above TARGET_BUILD_APPS

Even if we are doing TARGET_BUILD_APPS, we may want to use a cm
target for building.

Change-Id: Ic8053bc679fa8b726be90e611aeaacdf1850cabc
build: Optimizations

Change-Id: I23f367b542677aea2b2b1b82a6a4ff708df7e032