RFR: 8297036: Generalize C2 stub mechanism [v6]

[Roman Kennke]

> Currently, we have two implementations of out-of-line stubs in C2, one for safepoint poll stubs (C2SafepointPollStubTable in output.hpp) and another for nmmethod entry barriers (C2EntryBarrierStubTable in output.hpp). I will need a few more for Lilliput: One for checking lock-stack size in method prologue, one for handling lock failures (both for fast-locking), and another one for load-klass slow-path. It would be good to generalize the mechanism and consolidate the existing uses on the new general mechanism.
> 
> Testing:
>  - [x] tier1 (x86_64, x86_32, aarch64)
>  - [x] tier2 (x86_64, x86_32, aarch64)
>  - [x] tier3 (x86_64, x86_32, aarch64)

Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:

  More RISCV fixes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11188/files
  - new: https://git.openjdk.org/jdk/pull/11188/files/438f00f5..cdedf273

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11188&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11188&range=04-05

  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11188.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11188/head:pull/11188

PR: https://git.openjdk.org/jdk/pull/11188