RFR: Upstream merge jdk/jdk > sh/jdk to jdk-13+5

[Roman Kennke]

This completes the recent in-between merge up to tag jdk-13+5:

http://cr.openjdk.java.net/~rkennke/upstream-jdk13-merge-2019-01-25/changes.txt

Relevant stuff:

- 8217522: Missing barriers in some java_lang_String assertion code
after JDK-8217442
- 8217467: Access barriers are missing in C2 intrinsic for Base64

Testing: hotspot_gc_shenandoah as usual

Ok?