RFR: JDK-8305782: Provide MacroAssembler::breakpoint on aarch64 [v2]

[Thomas Stuefe]

> The ability to emit debug traps was useful for me on arm, and I miss it on aarch64.
> 
> Tested manually on Linux aarch64 in gdb with various values for hint covering the whole 16-bit range set. Hint gets encoded in the instruction (gdb decodes instruction as "BRK xxx" with xxx being the hint). According to documentation the hint ends up in ESR.ELx.ISS after the trap hit, but gdb refused to display the ESR register, so I could not verify that.

Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:

  reuse Assembler::brk

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13401/files
  - new: https://git.openjdk.org/jdk/pull/13401/files/bb5b3592..c9adf3bc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13401&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13401&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13401.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13401/head:pull/13401

PR: https://git.openjdk.org/jdk/pull/13401