Limit adb_test to first multilib

It uses libadb, which is also only compiled for the primary
architecture. BUILD_HOST_NATIVE_TEST is changing the default
LOCAL_MULTILIB to match BUILD_NATIVE_TEST.

Change-Id: Ia9c002e641125eb996a7f198af1f182d0d6171c6
diff --git a/adb/Android.mk b/adb/Android.mk
index cb6da62..9c8ab6d 100644
--- a/adb/Android.mk
+++ b/adb/Android.mk
@@ -207,6 +207,8 @@
 LOCAL_LDLIBS_windows := -lws2_32 -luserenv
 LOCAL_STATIC_LIBRARIES_windows := AdbWinApi
 
+LOCAL_MULTILIB := first
+
 include $(BUILD_HOST_NATIVE_TEST)
 
 # adb device tracker (used by ddms) test tool