RFR: Fix aarch64 after merge

[Roman Kennke]

http://cr.openjdk.java.net/~rkennke/fix-merge-aarch64-2/webrev.00/

Ok?


We should revise our merging+tagging process even more. It is not useful
to merge from upstream and tag it accordingly, only to clean up some
mess afterwards (PCH, aarch64) some of which is very cumbersome to do
during merge. E.g.:

- Merge from upstream up to the tag that we want (not to the tagging
changeset), get this reviewed and pushed
- Then test, fix fluff, esp. aarch64
- if this is ok, tag with shenandoah-jdk-XX+YY
- maybe pull in the tagging upstream changeset

Roman