RFR: 8252684: Move the AArch64 assember test under test/hotspot/gtest

[Nick Gasson]

There was a question on the SVE review thread on build-dev [1] a few
months ago about why there is a Python script and test code under
src/hotspot/cpu/aarch64. The script generates code to check the
Assembler instruction encodings against those of the system assembler.
The test runs every time the debug VM is started.

AFAIK there's no precedent in the rest of Hotspot for having functional
tests that run on startup, and we have the existing gtest framework for
testing internal C++ modules. This patch (perhaps more of an RFC) moves
the assembler test under test/hotspot/gtest/aarch64.

The test will now run in tier1, including for release builds. The
downside is that debug builds won't catch assembler encoding errors
immediately on startup.

Tested by injecting an error in one of the instruction encodings and
verifying `make test TEST="gtest"` fails.

[1] https://mail.openjdk.java.net/pipermail/build-dev/2020-August/028048.html

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Commit messages:
 - 8252684: Move the AArch64 assember test under test/hotspot/gtest

Changes: https://git.openjdk.java.net/jdk/pull/1476/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1476&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252684
  Stats: 2427 lines in 5 files changed: 1196 ins; 1227 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1476.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1476/head:pull/1476

PR: https://git.openjdk.java.net/jdk/pull/1476