[llvm] [LLVM][PDB] Use IsUnsigned flag for APInt correctly (PR #131598)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-sve-vls` running on `linaro-g3-04` while building `llvm` at step 3 "checkout".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/143/builds/6278

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 3 (checkout) failure: update (failure)
git version 2.34.1
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

```

</details>

https://github.com/llvm/llvm-project/pull/131598