Update MRI C Ruby extension to use new version of upb.

- Alter encode/decode paths to use the `upb_env` (environment)
  abstraction.
- Update upb amalgamation to upstream `93791bfe`.
- Fix a compilation warning (void*->char* cast).
- Modify build flags so that upb doesn't produce warnings -- the Travis
  build logs were pretty cluttered previously.

1 files changed, 4 insertions, 0 deletions

diff --git a/ruby/ext/google/protobuf_c/protobuf.h b/ruby/ext/google/protobuf_c/protobuf.h
index 985b7f3d..400909fe 100644
--- a/ruby/ext/google/protobuf_c/protobuf.h
+++ b/ruby/ext/google/protobuf_c/protobuf.h
@@ -511,6 +511,10 @@ VALUE enum_resolve(VALUE self, VALUE sym);
 const upb_pbdecodermethod *new_fillmsg_decodermethod(
     Descriptor* descriptor, const void *owner);
 
+// Maximum depth allowed during encoding, to avoid stack overflows due to
+// cycles.
+#define ENCODE_MAX_NESTING 63
+
 // -----------------------------------------------------------------------------
 // Global map from upb {msg,enum}defs to wrapper Descriptor/EnumDescriptor
 // instances.