RFR: 8286480: Remove the c1 getEventWriter() intrinsic to simplify post-Loom integration platform-porting efforts [v2]

[Markus Grönlund]

> Greetings,
> 
> The C1 intrinsic for getEventWriter() did not materialize and is currently only bouncing a platform-specific stub to enter the VM, putting an unnecessary burden on post-Loom integration platform-porting efforts.
> 
> The platform-specific stub for C2, jfr_write_checkpoint, is still needed but is only called if a java/lang/VirtualThread is mounted. As such, it could be left unimplemented.
> 
> Testing: jdk_jfr
> 
> Thanks
> Markus

Markus Grönlund has updated the pull request incrementally with two additional commits since the last revision:

 - missing comma
 - riscv

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8631/files
  - new: https://git.openjdk.java.net/jdk/pull/8631/files/4e38c4ba..c21ec34e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8631&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8631&range=00-01

  Stats: 20 lines in 1 file changed: 2 ins; 13 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8631.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8631/head:pull/8631

PR: https://git.openjdk.java.net/jdk/pull/8631