Export headers from libgif

Test: mmma -j external/skia
Change-Id: If89cd9a9d1b01068738ff8177870b4d0a5789795
diff --git a/Android.bp b/Android.bp
index 00bbf93..69cb704 100644
--- a/Android.bp
+++ b/Android.bp
@@ -18,4 +18,6 @@
         "-Wno-unused-parameter",
         "-DHAVE_CONFIG_H",
     ],
+
+    export_include_dirs: ["."],
 }