[turbofan] Disable one more failing mjsunit test.

TBR=rmcilroy@chromium.org

Review URL: https://codereview.chromium.org/1526983002

Cr-Commit-Position: refs/heads/master@{#32870}

test/mjsunit/mjsunit.status

@@ -1082,6 +1082,7 @@
   'regress/regress-78270': [SKIP],
   'regress/regress-91008': [SKIP],
   'regress/regress-crbug-347903': [SKIP],
+  'regress/regress-crbug-500497': [SKIP],
   'regress/regress-crbug-505007-1': [SKIP],
   'regress/regress-crbug-505007-2': [SKIP],
   'regress/short-circuit': [SKIP],