[ESNext] Activate async/await for ClusterFuzz

BUG=v8:4483
R=neis@chromium.org,littledan@chromium.org,caitpotter88@gmail.com
LOG=N

Review-Url: https://codereview.chromium.org/1992173002
Cr-Commit-Position: refs/heads/master@{#36362}

src/flag-definitions.h

@@ -195,6 +195,7 @@ DEFINE_NEG_VALUE_IMPLICATION(harmony_shipping, intl_extra, true)
 // Activate on ClusterFuzz.
 DEFINE_IMPLICATION(es_staging, harmony_regexp_lookbehind)
 DEFINE_IMPLICATION(es_staging, move_object_start)
+DEFINE_IMPLICATION(es_staging, harmony_async_await)
 
 // Features that are still work in progress (behind individual flags).
 #ifdef V8_I18N_SUPPORT