RFR: 8366062: [ubsan] add non-zero offset to nullptr in cds/archiveBuilder.cpp

[Afshin Zafari]

It is acceptable that the `SharedBaseAddress` option gets `0` at command line. The corresponding pointer arithmetic with `0` (`nullptr`) in archiveBuilder is UB.
Specific casts are used to avoid UBSAN error.

Tests:
linux-x64-debug: tier1 passed

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Commit messages:
 - 8366062: [ubsan] add non-zero offset to nullptr in cds/archiveBuilder.cpp

Changes: https://git.openjdk.org/jdk/pull/26983/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26983&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366062
  Stats: 12 lines in 1 file changed: 6 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/26983.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26983/head:pull/26983

PR: https://git.openjdk.org/jdk/pull/26983