update to NDK r17

We haven't done this in a while.

The only interesting change I've noticed so far is that we no longer
need to link libandroid_support when targeting API 21+.

Change-Id: I6506fbe7bd02534f1ea136f2164acab7f44c29e0
Reviewed-on: https://skia-review.googlesource.com/128009
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/gn/BUILD.gn b/gn/BUILD.gn
index 4c6eac2..ac036c2 100644
--- a/gn/BUILD.gn
+++ b/gn/BUILD.gn
@@ -169,8 +169,10 @@
     libs += [
       "c++_static",
       "c++abi",
-      "android_support",
     ]
+    if (ndk_api < 21) {
+      libs += [ "android_support" ]
+    }
   }
 
   if (is_ios) {