gn2bp: disable rtti in protobufs

libprotobuf is compiled with -fno-rtti, so disable it for all protobufs.

Test: //components/cronet/android:cronet
Change-Id: Ied846201a5cff765b464b846b38f4c2ae2ddda5d
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index 9ce33b8..e7028d1 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -1276,6 +1276,7 @@
   # Default settings used by all modules.
   defaults = Module('cc_defaults', defaults_module, '//gn:default_deps')
   defaults.cflags = [
+      '-DGOOGLE_PROTOBUF_NO_RTTI',
       '-Wno-error=return-type',
       '-Wno-non-virtual-dtor',
       '-Wno-macro-redefined',