Ported upb to C89, for greater portability.

A large part of this change contains surface-level
porting, like moving variable declarations to the
top of the block.

However there are a few more substantial things too:

- moved internal-only struct definitions to a separate
  file (structdefs.int.h), for greater encapsulation
  and ABI compatibility.

- removed the UPB_UPCAST macro, since it requires access
  to the internal-only struct definitions.  Replaced uses
  with calls to inline, type-safe casting functions.

- removed the UPB_DEFINE_CLASS/UPB_DEFINE_STRUCT macros.
  Class and struct definitions are now more explicit -- you
  get to see the actual class/struct keywords in the source.
  The casting convenience functions have been moved into
  UPB_DECLARE_DERIVED_TYPE() and UPB_DECLARE_DERIVED_TYPE2().

- the new way that we duplicate base methods in derived types
  is also more convenient and requires less duplication.
  It is also less greppable, but hopefully that is not
  too big a problem.

Compiler flags (-std=c89 -pedantic) should help to rigorously
enforce that the code is free of C99-isms.

A few functions are not available in C89 (strtoll).  There
are temporary, hacky solutions in place.

1 files changed, 3 insertions, 2 deletions

diff --git a/upb/bindings/googlepb/proto2.cc b/upb/bindings/googlepb/proto2.cc
index 87c13b6..636bb90 100644
--- a/upb/bindings/googlepb/proto2.cc
+++ b/upb/bindings/googlepb/proto2.cc
@@ -449,12 +449,13 @@ case goog::FieldDescriptor::cpptype:                                           \
     enum OneofType {
       ONEOF_TYPE_NONE,
       ONEOF_TYPE_STRING,
-      ONEOF_TYPE_MESSAGE,
+      ONEOF_TYPE_MESSAGE
 #ifdef UPB_GOOGLE3
+      ,
       ONEOF_TYPE_GLOBALSTRING,
       ONEOF_TYPE_CORD,
       ONEOF_TYPE_STRINGPIECE,
-      ONEOF_TYPE_LAZYFIELD,
+      ONEOF_TYPE_LAZYFIELD
 #endif
     };