RFR 8191988: TLAB Refills for S390

[JC Beyler]

Hi all,

The TLAB and the inline contiguous allocations handling are different
for each architecture. On certain architectures, TLAB is never
actually never refilled (ref:
https://bugs.openjdk.java.net/browse/JDK-8190862).

The S390 patch is a cleanup code webrev, it used to set the
allow_shared_alloc variable to false and then left code there. This
cleans it up and simplifies that code path.

Bug: https://bugs.openjdk.java.net/browse/JDK-8191988
WebRev: http://cr.openjdk.java.net/~rasbold/8191988/webrev.02/

Let me know what you think and if someone could test/verify it, that
would be great.

Thanks for your help,
Jc