[clang] [libc][nfc] Use common implementation of read_first_lane_u64 (PR #131027)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `openmp-s390x-linux` running on `systemz-1` while building `clang` at step 2 "checkout".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/88/builds/9054

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

```
Step 2 (checkout) failure: update (failure)
git version 2.34.1
fatal: unable to access 'https://github.com/llvm/llvm-project.git/': Failed to connect to github.com port 443 after 133598 ms: Connection timed out
fatal: unable to access 'https://github.com/llvm/llvm-project.git/': GnuTLS recv error (-110): The TLS connection was non-properly terminated.

```

</details>

https://github.com/llvm/llvm-project/pull/131027