RFR: 8257396: AArch64 Zero build is broken after JDK-8252684

[Aleksey Shipilev]

Zero does not have AArch64 assembler, so attempt to use it from the test fails to build. The fix is trivial: sense if we are building Zero.

Testing:
 - [x] Linux aarch64 zero build

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Commit messages:
 - 8257396: AArch64 Zero build is broken after JDK-8252684

Changes: https://git.openjdk.java.net/jdk/pull/1511/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1511&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257396
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1511.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1511/head:pull/1511

PR: https://git.openjdk.java.net/jdk/pull/1511