build: no longer build emulator by default

This is just increasing build times when most people are not using it.
Let's speed up builds a bit.

Building emulator should still be possible by appending BUILD_EMULATOR=true
to the build command

Change-Id: Ibd8e2b90455bd603a691c7b95466068b6fae212a
envsetup: enable gcc colours for warnings/errors

Change-Id: I1f6e9dab9029cbee6d4a1e6ce383d7b9e9fa2b3a
Signed-off-by: zwliew <zhaoweiliew@gmail.com>