RFR: JDK-8324682 Remove redefinition of NULL for XLC compiler [v2]

[Suchismith Roy]

> Remove redefinition of NULL for XLC compiler
> 
> JBS ISSUE : [JDK-8324682](https://bugs.openjdk.org/browse/JDK-8324682)

Suchismith Roy has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Redefine NULL word

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18064/files
  - new: https://git.openjdk.org/jdk/pull/18064/files/630144ce..eb8faf93

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18064&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18064&range=00-01

  Stats: 226 lines in 1 file changed: 0 ins; 226 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18064.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18064/head:pull/18064

PR: https://git.openjdk.org/jdk/pull/18064