RFR: 8334475: UnsafeIntrinsicsTest.java#ZGenerationalDebug assert(!assert_on_failure) failed: Has low-order bits set

[Saint Wesonga]

The implementation of the pd_conjoint_jlongs_atomic function in the Windows AArch64 port calls pd_conjoint_oops_atomic to copy jlongs from the source to the destination. However, when CHECK_UNHANDLED_OOPS is defined, copying of each jlong in pd_conjoint_oops_atomic calls oop::operator= instead of just copying the jlong.

oop::operator= then treats the value to be copied as a pointer, causing the assertion failure in JDK-8334475. The fix is to directly copy the jlongs from the source to the destination. The test "compiler/gcbarriers/UnsafeIntrinsicsTest.java" now passes on the Windows AArch64 port.

This PR also cleans up code duplication (similar to how  https://github.com/openjdk/jdk/pull/12197 cleaned it up when fixing jlong copying for Windows x64).

-------------

Commit messages:
 - Fix code duplication
 - Directly copy jlongs on Windows AArch64

Changes: https://git.openjdk.org/jdk/pull/20390/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20390&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334475
  Stats: 57 lines in 1 file changed: 17 ins; 36 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/20390.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20390/head:pull/20390

PR: https://git.openjdk.org/jdk/pull/20390