RFR: JDK-8300651: Replace NULL with nullptr in share/runtime/

[Johan Sjölen]

Do the conversion in the share/runtime/ sub-directory and all of its files.

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Commit messages:
 - More manual fixes
 - fixes
 - Fixes
 -  Replace NULL with nullptr in share/runtime/

Changes: https://git.openjdk.org/jdk/pull/12094/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12094&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300651
  Stats: 2071 lines in 112 files changed: 0 ins; 0 del; 2071 mod
  Patch: https://git.openjdk.org/jdk/pull/12094.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12094/head:pull/12094

PR: https://git.openjdk.org/jdk/pull/12094