emulator: api 26 fix guest rendering (build)

As swiftshader is open sourced, put it into emulator
targets to enable -gpu guest option.

Test: build aosp_x86-eng, launch emulator -gpu guest
and it should boot to home screen.

Change-Id: I2140d7cec28d5f00b7463b1d37d9cf62120398fb
4 files changed