[OCaml] Update api to account for FNeg and CallBr instructions

[jberdine]

Summary

This diff adds minimal support for the recent FNeg and CallBr
instructions to the OCaml bindings.

[whitequark]

LGTM

[jberdine]

Thanks! Could I bother you to commit this?

bindings/ocaml/llvm/llvm.ml

module Opcode  = struct
   | Resume
   | LandingPad
   | AddrSpaceCast
   | CleanupRet
   | CatchRet
   | CatchPad
   | CleanupPad
   | CatchSwitch
+  | FNeg
+  | CallBr
 end
 
 module LandingPadClauseTy = struct
   type t =
   | Catch
   | Filter
 end
 

bindings/ocaml/llvm/llvm.mli

module Opcode : sig
   | Resume
   | LandingPad
   | AddrSpaceCast
   | CleanupRet
   | CatchRet
   | CatchPad
   | CleanupPad
   | CatchSwitch
+  | FNeg
+  | CallBr
 end
 
 (** The type of a clause of a [landingpad] instruction.
     See [llvm::LandingPadInst::ClauseType]. *)
 module LandingPadClauseTy : sig
   type t =
   | Catch
   | Filter

bindings/ocaml/llvm/llvm_ocaml.c

DEFINE_ITERATORS(instr, Instruction, LLVMBasicBlockRef, LLVMValueRef,
                  LLVMGetInstructionParent)
 
 /* llvalue -> Opcode.t */
 CAMLprim value llvm_instr_get_opcode(LLVMValueRef Inst) {
   LLVMOpcode o;
   if (!LLVMIsAInstruction(Inst))
       failwith("Not an instruction");
   o = LLVMGetInstructionOpcode(Inst);
-  assert (o <= LLVMCatchSwitch);
+  assert (o <= LLVMCallBr);
   return Val_int(o);
 }
 
 /* llvalue -> ICmp.t option */
 CAMLprim value llvm_instr_icmp_predicate(LLVMValueRef Val) {
   CAMLparam0();
   int x = LLVMGetICmpPredicate(Val);
   if (x) {