RFR: 8319883: Zero: Use atomic built-ins for 64-bit accesses

[Aleksey Shipilev]

See the bug for reproducer and discussion.

This reimplements related Zero parts using `__atomic_*`: we already use some of those both in Atomic and around Hotspot code. As far as I can see from both GCC and LLVM docs, these would be translated to proper accesses on all target platforms. Doing even the relaxed atomic access for 64-bit platforms is probably an overkill, but for Zero we want baseline correctness first and foremost.

Example current uses of `__atomic_load` on both BSD (I think it assumes clang) and Linux (assumes GCC):
https://github.com/openjdk/jdk/blob/a64fc48e2dbc650b31869dd79b1ba1012376fc51/src/hotspot/os_cpu/bsd_aarch64/atomic_bsd_aarch64.hpp#L115
https://github.com/openjdk/jdk/blob/a64fc48e2dbc650b31869dd79b1ba1012376fc51/src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.hpp#L203
https://github.com/openjdk/jdk/blob/a64fc48e2dbc650b31869dd79b1ba1012376fc51/src/hotspot/os_cpu/linux_riscv/atomic_linux_riscv.hpp#L172

Additional testing:
 - [x] MacOS AArch64 Zero fastdebug; light jcstress tests still pass
 - [x] Linux x86_32 Zero release; previously failing jcstress testing now passes
 - [x] Linux x86_32 Zero fastdebug, `compiler/unsafe java/lang/invoke/VarHandles`
 - [x] Linux x86_32 Zero fastdebug, bootcycle-images

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Commit messages:
 - Reinstate casts where need, drop casts where not needed
 - LLVM/BSD versions and harmonize with GCC
 - Fix

Changes: https://git.openjdk.org/jdk/pull/16600/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16600&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319883
  Stats: 63 lines in 2 files changed: 0 ins; 48 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/16600.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16600/head:pull/16600

PR: https://git.openjdk.org/jdk/pull/16600