Export libbinder headers from libhealhd.default

Consumers of libhealthd.default will need these headers.

Bug: 27804373
Change-Id: I59e8526e3491f0db528d1277b8e2f4b68ce85805
Test: Compiles.
diff --git a/healthd/Android.mk b/healthd/Android.mk
index d866887..127f39e 100644
--- a/healthd/Android.mk
+++ b/healthd/Android.mk
@@ -9,6 +9,7 @@
 LOCAL_C_INCLUDES := $(LOCAL_PATH)/include
 LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/include
 LOCAL_STATIC_LIBRARIES := libbinder
+LOCAL_EXPORT_STATIC_LIBRARY_HEADERS := libbinder
 include $(BUILD_STATIC_LIBRARY)
 
 include $(CLEAR_VARS)