Enable host multilib for ART testing.

Change-Id: Ic3ae5122eba13565fb5a4cb1bd0e7e465fb2140c
diff --git a/libbacktrace/Android.mk b/libbacktrace/Android.mk
index 74bae1a..1de81e7 100755
--- a/libbacktrace/Android.mk
+++ b/libbacktrace/Android.mk
@@ -113,7 +113,9 @@
 build_target := SHARED_LIBRARY
 include $(LOCAL_PATH)/Android.build.mk
 build_type := host
+libbacktrace_libc++_multilib := both
 include $(LOCAL_PATH)/Android.build.mk
+libbacktrace_libc++_multilib :=
 endif
 
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