Add an informative comment on regress-1132 ASAN suppression

TBR=arv@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/1199053002.

Cr-Commit-Position: refs/heads/master@{#29205}

test/mjsunit/mjsunit.status

@@ -408,6 +408,8 @@
   'big-array-literal': [SKIP],
   'big-object-literal': [SKIP],
   'regress/regress-crbug-178790': [SKIP],
+
+  # Exception thrown during bootstrapping on ASAN builds, see issue 4236.
   'regress/regress-1132': [SKIP],
 }],  # 'asan == True'