Fix d8-os unit test to be skipped for isolates.

test/mjsunit/mjsunit.status

Index: test/mjsunit/mjsunit.status
diff --git a/test/mjsunit/mjsunit.status b/test/mjsunit/mjsunit.status
index 186c2a465b1f9ac749e5c14cae43f71b518d5925..2d22fe9075063812e75315eb187eb823254d8451 100644
--- a/test/mjsunit/mjsunit.status
+++ b/test/mjsunit/mjsunit.status
@@ -66,6 +66,13 @@ debug-liveedit-check-stack: SKIP
 debug-liveedit-patch-positions-replace: SKIP
 
 ##############################################################################
+[ $isolates ]
+
+# This test sets the umask on a per-process basis and hence cannot be
+# used in multi-threaded runs.
+d8-os: SKIP
+
+##############################################################################
 [ $arch == arm ]
 
 # Slow tests which times out in debug mode.