RFR: 8253795: Implementation of JEP 391: macOS/AArch64 Port [v10]

[Anton Kozlov]

> Please review the implementation of JEP 391: macOS/AArch64 Port.
> 
> It's heavily based on existing ports to linux/aarch64, macos/x86_64, and windows/aarch64. 
> 
> Major changes are in:
> * src/hotspot/cpu/aarch64: support of the new calling convention (subtasks JDK-8253817, JDK-8253818)
> * src/hotspot/os_cpu/bsd_aarch64: copy of os_cpu/linux_aarch64 with necessary adjustments (JDK-8253819)
> * src/hotspot/share, test/hotspot/gtest: support of write-xor-execute (W^X), required on macOS/AArch64 platform. It's implemented with pthread_jit_write_protect_np provided by Apple. The W^X mode is local to a thread, so W^X mode change relates to the java thread state change (for java threads). In most cases, JVM executes in write-only mode, except when calling a generated stub like SafeFetch, which requires a temporary switch to execute-only mode. The same execute-only mode is enabled when a java thread executes in java or native states. This approach of managing W^X mode turned out to be simple and efficient enough.
> * src/jdk.hotspot.agent: serviceability agent implementation (JDK-8254941)

Anton Kozlov has updated the pull request incrementally with six additional commits since the last revision:

 - Merge remote-tracking branch 'origin/jdk/jdk-macos' into jdk-macos
 - Add comments to WX transitions
   
   + minor change of placements
 - Use macro conditionals instead of empty functions
 - Add W^X to tests
 - Do not require known W^X state
 - Revert w^x in gtests

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2200/files
  - new: https://git.openjdk.java.net/jdk/pull/2200/files/3c705ae5..80827176

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2200&range=09
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2200&range=08-09

  Stats: 444 lines in 64 files changed: 112 ins; 278 del; 54 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2200.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2200/head:pull/2200

PR: https://git.openjdk.java.net/jdk/pull/2200