[llvm] [AMDGPU][Attributor] Make `AAAMDFlatWorkGroupSize` honor existing attribute (PR #114357)

[John Tramm via llvm-commits]

jtramm wrote:

Here's what my current cmake line looks like for LLVM:

```
PROJECTS="clang;lld"
RUNTIMES="openmp;offload"
TARGETS="all"
USE_CCACHE=OFF

cmake \
    -DCMAKE_C_COMPILER=clang \
    -DCMAKE_CXX_COMPILER=clang++ \
    -DLLVM_ENABLE_PROJECTS=${PROJECTS}  \
    -DLLVM_ENABLE_RUNTIMES=${RUNTIMES}   \
    -DLLVM_TARGETS_TO_BUILD=${TARGETS}   \
    -DLLVM_ENABLE_ASSERTIONS=ON \
    -DLIBOMPTARGET_ENABLE_DEBUG=ON \
    -DLLVM_OPTIMIZED_TABLEGEN=ON \
    -DBUILD_SHARED_LIBS=ON \
    -DLLVM_CCACHE_BUILD=${USE_CCACHE} \
    -DLLVM_APPEND_VC_REV=OFF \
    -DCMAKE_BUILD_TYPE=RelWithDebInfo \
    -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
    -DCMAKE_CXX_FLAGS="-Wno-address" \
    -DCMAKE_INSTALL_PREFIX=../llvm-install \
    ../llvm-project/llvm

make -j128 install
```

What would I need to change to specifically rebuild the device libraries, or am I already doing that?

https://github.com/llvm/llvm-project/pull/114357