Mirror the rather significant changes in Android.mk from:
https://github.com/KhronosGroup/SPIRV-Tools/commit/64f36ea5296ec023f65f75d72196d3ff7ae7c7b2?diff=split

Bug: b/123642959
Change-Id: Iaf82487e768dd0062a97cfe8ebff4e7f85816141
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/39876Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Ben Clayton <bclayton@google.com>