RFR: 8342011: Conditionally compile ReservedHeapSpace compressed heap support [v2]

[Kim Barrett]

> Please review this change to ReservedHeapSpace to conditionally include the
> support for compressed oops only in 64bit builds.  This code is unused and
> inapplicable in 32bit builds.  Further, it contains code that is problematic
> in a 32bit build.  See the JBS issue for details.
> 
> Testing: mach5 tier1, GHA testing

Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:

  improve conditionalization

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21484/files
  - new: https://git.openjdk.org/jdk/pull/21484/files/627b75ee..82c6846d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21484&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21484&range=00-01

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21484.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21484/head:pull/21484

PR: https://git.openjdk.org/jdk/pull/21484