Include toolchain makefile based on the current config.

So we can have the same set of module names in different host arch
/ toolchain version combinations.

Change-Id: Iec66584bf3de92aedd71a59f9dbe74b6ed025b2e
diff --git a/libs/host/Android.mk b/libs/host/Android.mk
index d02e4b2..9900f59 100644
--- a/libs/host/Android.mk
+++ b/libs/host/Android.mk
@@ -23,3 +23,5 @@
 
 include $(BUILD_HOST_STATIC_LIBRARY)
 
+# Include toolchain prebuilt modules if they exist.
+-include $(TARGET_TOOLCHAIN_ROOT)/toolchain.mk