add -ldl to host executables

This fixes the build on Linux when RefBase is compiled with reference tracking
enabled.

Change-Id: I3e931e0b463ce836f6fdb30c37068d77144631a3
Signed-off-by: Iliyan Malchev <malchev@google.com>
diff --git a/libs/utils/Android.mk b/libs/utils/Android.mk
index 638f72f..831d9e3 100644
--- a/libs/utils/Android.mk
+++ b/libs/utils/Android.mk
@@ -71,6 +71,10 @@
 endif
 endif
 
+ifeq ($(TARGET_OS),linux)
+LOCAL_LDLIBS += -lrt -ldl
+endif
+
 include $(BUILD_HOST_STATIC_LIBRARY)