Add options for building/testing with coverage.

    acov --clean
    mm -B NATIVE_COVERAGE=true ART_COVERAGE=true test-art-host
    acov --host

-B is needed because you need to be sure you rebuild *all* of ART with
coverage.

Change-Id: Ib94ef610bd1b44dc45624877710ed733051b7a50
diff --git a/sigchainlib/Android.mk b/sigchainlib/Android.mk
index e0f1769..e1aae11 100644
--- a/sigchainlib/Android.mk
+++ b/sigchainlib/Android.mk
@@ -28,6 +28,7 @@
 LOCAL_SHARED_LIBRARIES := liblog
 LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/Android.mk
 LOCAL_ADDITIONAL_DEPENDENCIES += art/build/Android.common_build.mk
+LOCAL_NATIVE_COVERAGE := $(ART_COVERAGE)
 $(eval $(call set-target-local-clang-vars))
 include $(BUILD_SHARED_LIBRARY)
 
@@ -56,6 +57,7 @@
 LOCAL_ADDITIONAL_DEPENDENCIES += $(LOCAL_PATH)/Android.mk
 LOCAL_LDLIBS = -ldl
 LOCAL_MULTILIB := both
+LOCAL_NATIVE_COVERAGE := $(ART_COVERAGE)
 include $(BUILD_HOST_SHARED_LIBRARY)
 
 include $(CLEAR_VARS)