Refactor the compilers out of libart.

This builds three separate compilers and dynamically links with the right one
at runtime.

Change-Id: I59d22b9884f41de733c09f97e29ee290236d5f4b
diff --git a/Android.mk b/Android.mk
index 02080cc..168b619 100644
--- a/Android.mk
+++ b/Android.mk
@@ -27,6 +27,7 @@
 include $(build_path)/Android.common.mk
 
 include $(build_path)/Android.libart.mk
+include $(build_path)/Android.libart-compiler.mk
 include $(build_path)/Android.executable.mk
 
 include $(build_path)/Android.oat.mk