[lworld] RFR: 8312231: Replacing NULL with nullptr in shared code

[Frederic Parain]

This patch applies the NULL -> nullptr transition to shared code.

Builds tested with Mach5 (tier1).

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Commit messages:
 - Replacing NULL with nullptr

Changes: https://git.openjdk.org/valhalla/pull/886/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=886&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8312231
  Stats: 309 lines in 63 files changed: 0 ins; 0 del; 309 mod
  Patch: https://git.openjdk.org/valhalla/pull/886.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/886/head:pull/886

PR: https://git.openjdk.org/valhalla/pull/886