RFR: 8298088: RISC-V: Make Address a discriminated union internally [v2]

[Fei Yang]

> The RISC-V port has the same issue as: https://bugs.openjdk.org/browse/JDK-8297830
> It looks to me that the fix for the AArch64 port is a nice refactoring work.
> This fixes this issue for the RISC-V port with a similar approach.
> 
> Testing:
>   Tier1 tested with release build on linux-riscv64 unmatched board.
>   Run non-trivial benchmark workloads with fastdebug builds.

Fei Yang has updated the pull request incrementally with one additional commit since the last revision:

  Review

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11505/files
  - new: https://git.openjdk.org/jdk/pull/11505/files/ab1b8401..3cbfe94f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11505&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11505&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11505.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11505/head:pull/11505

PR: https://git.openjdk.org/jdk/pull/11505