RFR: 8253795: Implementation of JEP 391: macOS/AArch64 Port [v20]

[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 two additional commits since the last revision:

 - Merge pull request #10 from VladimirKempik/pull/2200
   
   Fix build after merge with master
 - Fix build after merge with master

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2200/files
  - new: https://git.openjdk.java.net/jdk/pull/2200/files/74687c0b..241aedee

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2200&range=19
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2200&range=18-19

  Stats: 7 lines in 1 file changed: 0 ins; 1 del; 6 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