[8u] RFR: JDK-8253036: Support building the Zero assembler port on AArch64

[Andrew Hughes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8253036
Webrev: https://cr.openjdk.java.net/~andrew/openjdk8/8253036/webrev.01/

This patch contains the minimal changes necessary for the Zero assembler
port (--with-jvm-variants=zero) to build on AArch64.

The changes are a subset of JDK-8064611, which also contains changes
for the AArch64 port.

I intend to follow this with a single patch to bring in the current
state of the AArch64 port. This patch reduces the shared code changes
in that upcoming patch and gives us a useful starting point of being
able to build 8u on AArch64.

Ok for 8u-dev?

Thanks,
-- 
Andrew :)

Senior Free Java Software Engineer
OpenJDK Package Owner
Red Hat, Inc. (http://www.redhat.com)

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