Fix build warning.

Change-Id: Ia7f157116fddec710fce0ec3d187bbcac18fab12

tests/Android.mk

diff --git a/tests/Android.mk b/tests/Android.mk
index 68d0765..189572c 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -52,7 +52,7 @@
 ifeq ($(HOST_OS),linux)
 # Compile using the host only on linux for valgrind support.
 define host-test
-$(call _define-test,$(1),eng,HOST_,-O0 -g,_host)
+$(call _define-test,$(1),optional,HOST_,-O0 -g,_host)
 endef
 endif