RFR: 8367692: RISC-V: Align post call nop

[Robbin Ehn]

Hi please, consider.

As ziccif require instructions to natural aligned to be atomic the 4 byte post call nop must be aligned.
But I don't want to add a c.nop(2b) to align the nop(4b) which means the jal(r) must also be algined.
As we have no utility to aligned the end of an instruction sequence the call it self is aligned and uses only 4 byte instructions. Only in the case where we could use an two c-instruction we may loose space.

Thanks, Robbin

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Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/27467/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27467&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367692
  Stats: 137 lines in 7 files changed: 76 ins; 28 del; 33 mod
  Patch: https://git.openjdk.org/jdk/pull/27467.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27467/head:pull/27467

PR: https://git.openjdk.org/jdk/pull/27467