Sync up with wabt latest modification (#296) (#786)

- Remove "--enable-reference-types" and "--enable-bulk-memory" for wat2wasm
to support finished proposals.

- Ignore invalid module in the thread spec repo:
``` wast
;; my_elem.wast
(module
  (table $t 10 funcref)
  (func $f)
  (elem $t (i32.const 0) 0)
  (elem $t (i32.const 0) $f $f)
  (elem $t (offset (i32.const 0)) $f $f)
)
```

run with reference interpreter under spec/interpreter:
``` shell
$ ./wasm ../../../my_elem.wast
../../../my_elem.wast:5.9-5.11: syntax error: duplicate elem segment $t
```

- use a specific commit instead of the latest commit on the thread spec repo

tests/wamr-test-suites/spec-test-script/runtest.py

@@ -901,10 +901,9 @@ def compile_wast_to_wasm(form, wast_tempfile, wasm_tempfile, opts):
             "--no-check",
             wast_tempfile, "-o", wasm_tempfile ]
 
-    # optional arguments
-    if opts.ref_types:
-        cmd.append("--enable-reference-types")
-        cmd.append("--enable-bulk-memory")
+    # remove reference-type and bulk-memory enabling options since a WABT
+    # commit 30c1e983d30b33a8004b39fd60cbd64477a7956c
+    # Enable reference types by default (#1729)
 
     log("Running: %s" % " ".join(cmd))
     try: