RFR: 8366062: [ubsan] add non-zero offset to nullptr in cds/archiveBuilder.cpp [v2]

[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

Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:

  comments improved

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26983/files
  - new: https://git.openjdk.org/jdk/pull/26983/files/531a47d1..6beeecb3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26983&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26983&range=00-01

  Stats: 5 lines in 1 file changed: 0 ins; 0 del; 5 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