Blacklist regress-3960 from turbofan.

TBR=adamk@chromium.org
BUG=v8:4325,chromium:513160
LOG=N

Review URL: https://codereview.chromium.org/1259863003

Cr-Commit-Position: refs/heads/master@{#29863}

test/mjsunit/mjsunit.status

@@ -152,6 +152,9 @@
   # issue 4078:
   'allocation-site-info': [PASS, NO_VARIANTS],
 
+  # issue 4325:
+  'regress/regress-3960': [PASS, NO_VARIANTS],
+
   ##############################################################################
   # Too slow in debug mode with --stress-opt mode.
   'compiler/regress-stacktrace-methods': [PASS, ['mode == debug', SKIP]],