[clang] [Clang] Fix createConstexprUnknownAPValues to use zero offset when ceating APValue (PR #124478)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

No Release notes b/c this is a fix for https://github.com/llvm/llvm-project/pull/95474 which has its own release note.

Tests for this fix will be added by https://github.com/llvm/llvm-project/pull/124476

https://github.com/llvm/llvm-project/pull/124478