RFR: 8366062: [ubsan] add non-zero offset to nullptr in cds/archiveBuilder.cpp [v8]

[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:

  suggested change is applied. one error is addressed. one remains still.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26983/files
  - new: https://git.openjdk.org/jdk/pull/26983/files/5b0dbb9e..efe3d469

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26983&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26983&range=06-07

  Stats: 4 lines in 1 file changed: 0 ins; 1 del; 3 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