Add the exported include directory for libunwind.

Change-Id: Icb5a22d2099d15fd97318985d4d39e0b2c646f0d
diff --git a/Android.mk b/Android.mk
index b6ecc09..88a65b0 100644
--- a/Android.mk
+++ b/Android.mk
@@ -47,4 +47,5 @@
 LOCAL_MODULE_TARGET_ARCH := arm
 LOCAL_CXX_STL := none
 LOCAL_SANITIZE := never
+LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/include
 include $(BUILD_STATIC_LIBRARY)