RFR: 8335298: Fix -Wzero-as-null-pointer-constant warning in G1CardSetContainers [v2]

[Kim Barrett]

> Please review this change to the G1CardSetInlinePtr default constructor to
> avoid -Wzero-as-null-pointer-constant.  The problem is that it is casting a
> constant 0 to a pointer.  Because casting 0 to a pointer is what this code
> needs to do, the options are to (1) suppress the warning, or (2) write the
> code in such a way as to dodge the warning.  We take the latter approach, as
> it involves less source code clutter.  We expect an optimizing compiler to
> produce the same code either way.
> 
> Also simplified the constructors by using delegation.
> 
> Testing: mach5 tier1.
> Locally (linux-x64) verified the warning no longer occurs with this change.

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

  change comment to refer to gcc bug

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19955/files
  - new: https://git.openjdk.org/jdk/pull/19955/files/08d3cc88..cbe06d22

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19955&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19955&range=00-01

  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/19955.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19955/head:pull/19955

PR: https://git.openjdk.org/jdk/pull/19955