Build: Add Custom Toolchain Support

* Many legacy devices don't support 4.8 so we need a 4.7 option and many of the newer devices do better either Linaro 4.8 or SM 4.8-4.10 so this just makes sense. Same flag as KitKat Liquid.

Signed-off-by: Chet Kener <Cl3Kener@gmail.com>
Change-Id: Ibf5a1204392214244b93316cc05bc715bf3b81bf
Signed-off-by: Chet Kener <Cl3Kener@gmail.com>

Conflicts:
	core/tasks/kernel.mk
Merge branch 'psoa_r2' of https://github.com/EuclideanROM/platform_build into psoa_r2