Fix potential makefile bug.

Since multilib is not set every time, it needs to be per module or
there is a change that another target will use the multilib value set
previously.

Change-Id: I5c30e18d5111705cb3f6e3d4cd9ef8a28c9b746c
diff --git a/tests/Android.mk b/tests/Android.mk
index 0014af6..d85e8eb 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -221,7 +221,7 @@
 
 module := bionic-unit-tests
 module_tag := optional
-multilib := both
+bionic-unit-tests_multilib := both
 build_type := target
 build_target := NATIVE_TEST
 include $(LOCAL_PATH)/Android.build.mk
@@ -243,7 +243,7 @@
 
 module := bionic-unit-tests-static
 module_tag := optional
-multilib := both
+bionic-unit-tests-static_multilib := both
 build_type := target
 build_target := NATIVE_TEST
 include $(LOCAL_PATH)/Android.build.mk