Roll llvm-libc from 96508da3edeb to 620afacd794f (7 revisions)

https://chromium.googlesource.com/external/github.com/llvm/llvm-project/libc.git/+log/96508da3edeb..620afacd794f

2025-08-09 huberjn@outlook.com [libc] Fix server code when GPU is acting as the server
2025-08-08 kpandey81930@gmail.com [libc][math][c++23] Add f{max,min}bf16 math functions (#152782)
2025-08-08 kpandey81930@gmail.com [libc][math] Update entrypoints for bf16{add,sub}{,f,l,f128} math functions (#152784)
2025-08-08 huberjn@outlook.com [libc] Cache old slabs when allocating GPU memory (#151866)
2025-08-08 kpandey81930@gmail.com [libc][math][c++23] Add bf16{add,sub}{,f,l,f128} math functions (#152774)
2025-08-08 60100307+bassiounix@users.noreply.github.com [libc][hdrgen] Fix hdrgen when using macros as guards in stdlib.yaml. (#152732)
2025-08-08 60100307+bassiounix@users.noreply.github.com [libc][math] Refactor cbrtf implementation to header-only in src/__support/math folder. (#151846)

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Change-Id: I338adf543b01dead4875486626cb4333dec3d84e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6834085
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