RFR: 8324686: Remove redefinition of NULL for MSVC

[Kim Barrett]

Please review this change that removes the redefinition of NULL in
globalDefinitions_visCPP.hpp. That redefinition was to support the use of NULL
in a varargs context, because of the size difference for int vs a pointer.
However, we no longer have any direct uses of NULL in HotSpot, and have a test
that ensures there is no backsliding.

There may be indirect uses of NULL via third-party libraries.  Such uses could
have been in the scope of the removed redefinition.  But those uses must have
been correct even without the redefinition, else they would be incorrect for
non-HotSpot users.

Testing: mach5 tier1-3, GHA sanity tests

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Commit messages:
 - remove VS redef of NULL

Changes: https://git.openjdk.org/jdk/pull/24537/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24537&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324686
  Stats: 21 lines in 2 files changed: 0 ins; 20 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24537.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24537/head:pull/24537

PR: https://git.openjdk.org/jdk/pull/24537