Make wasm-opt generate the new exception handling instructions

Author: vouillon

compiler/lib/wasm/wa_binaryen.ml

@@ -123,6 +123,7 @@ let optimize ~profile ~opt_input_sourcemap ~input_file ~opt_output_sourcemap ~ou
   in
   command
     ("wasm-opt"
+     :: "--emit-exnref"
      :: (common_options ()
         @ optimization_options.(level - 1)
         @ [ Filename.quote input_file; "-o"; Filename.quote output_file ])