[llvm-branch-commits] [libc] Use UMAXV.4S to reduce bcmp result. (PR #99260)

[Peter Collingbourne via llvm-branch-commits]

pcc wrote:

 can't reproduce this test failure. I did:
```
cmake -G Ninja -DLLVM_ENABLE_RUNTIMES=libc -DLLVM_ENABLE_PROJECTS=clang\;lld -DCMAKE_BUILD_TYPE=RelWithDebInfo -DLLVM_ENABLE_ASSERTIONS=1 -DLLVM_TARGETS_TO_BUILD=AArch64 -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ ../llvm
ninja libc
ninja -C ./runtimes/runtimes-bins check-libc
```
all tests passed.

https://github.com/llvm/llvm-project/pull/99260