turn exceptions on in test tools on Android

This is a follow-up to https://skia-review.googlesource.com/c/34982
which did the same for locally built test tools.

Change-Id: Id97841a64521fda99cb952a1a751ffc10f636f53
Reviewed-on: https://skia-review.googlesource.com/35162
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>

gn/gn_to_bp.py

@@ -15,6 +15,7 @@ import subprocess
 import tempfile
 
 tool_cflags = [
+    '-fexceptions',
     '-Wno-unused-parameter',
 ]