RFC: Pick up jdk/jdk -> sh/jdk at jdk-13+20+

[Roman Kennke]

Yep, let's do it!

Thanks,
Roman

> We need to pick up latest jdk/jdk for nofwdptr and x86_32 stabilization. Last week's jdk/jdk was
> riddled with build/test failures, which seem to be resolved at current state. I don't think we want
> to risk waiting for another tag, and instead merge at latest buildable changeset:
> 
> changeset:   55778:d7819bedfaaf
> tag:         tip
> user:        redestad
> date:        Tue May 14 12:00:49 2019 +0200
> summary:     8221478: Disable VerifySharedSpaces by default
> 
> There is one lingering fastdebug/accounting bug not fixed:
>   https://bugs.openjdk.java.net/browse/JDK-8223502
> 
> ...but again, it seems dubious to wait for it, as jdk/jdk may regress. I would deal with that bug
> upstream as soon as possible. We would hopefully catch jdk-13+21 on Thursday as the follow-up.
> 
> This merge changesets:
>   http://cr.openjdk.java.net/~shade/shenandoah/merges/jdk-13%2b20-plus/changesets.txt
> 
> Brings in:
>   8222992: Shenandoah: Pre-evacuate all roots
>   8223258: Shenandoah: SRP::process_all_roots_slow processes JvmtiExport weak oops twice
>   8223389: Shenandoah optimizations fail with assert(!phase->exceeding_node_budget())
>   8222738: Shenandoah: assert(is_Proj()) failed when running cometd benchmarks
>   8223448: Shenandoah disabled barriers blocks omit LRB
>   8223450: Disable Shenandoah C2 barriers verification for x86_32
>   8223449: Unprotected UseCompressedOops block in gc/shenandoah/shenandoahBarrierSetC1_x86.cpp
>   8223446: Shenandoah breaks alignment with some HumongousThreshold values
>   8223447: Stabilize gc/shenandoah/TestStringDedupStress test
>   8223570: Shenandoah needs to acquire lock before CLDG::clear_claimed_marks
>   8222926: Shenandoah build fails with --with-jvm-features=-compiler1
>   8223567: Rename ShenandoahBrooksPointer to ShenandoahForwarding
>   8223583: Build failure after JDK-8223567 (Rename ShenandoahBrooksPointer to ShenandoahForwarding)
>   8223427: [TESTBUG] Disable JTReg Shenandoah tests when Graal is enabled
>   8223759: Shenandoah should allow arbitrarily low initial heap size
>   8223762: Shenandoah: overflows in calculations involving heap capacity
> 
> This merge webrev:
>   http://cr.openjdk.java.net/~shade/shenandoah/merges/jdk-13%2b20-plus/webrev.01/
> 
> I also eyeballed that current sh/jdk diff does not miss anything from nofwdptr patch.
> 
> Testing: hotspot_gc_shenandoah {fastdebug|release}
>