RFR(T): 8239931: [win][x86] vtable stub generation: assert failure (code size estimate) follow-up

[Schmidt, Lutz]

All, 

please review this change to increase the size estimate (for a cmpl instruction) in the vtable stub generator. I would categorize this change as trivial. 

This fix is a follow-up to JDK-8239456. 

Testing: SAP-internal nightly tests (which showed the assert failure)
         jdk/submit (pending)

Bug:    https://bugs.openjdk.java.net/browse/JDK-8239931
Webrev: http://cr.openjdk.java.net/~lucy/webrevs/8239931.00/ 

Thanks,
Lutz