[llvm] [AMDGPU] Intrinsic for launching whole wave functions (PR #145859)

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

This may have turned our HIP blender bot red: https://lab.llvm.org/buildbot/#/builders/123/builds/24793

```
[34/59] Building CXX object External/HIP/CMakeFiles/TheNextWeek-hip-6.3.0.dir/workload/ray-tracing/TheNextWeek/main.cc.o
FAILED: External/HIP/CMakeFiles/TheNextWeek-hip-6.3.0.dir/workload/ray-tracing/TheNextWeek/main.cc.o 
/home/botworker/bbot/clang-hip-vega20/botworker/clang-hip-vega20/llvm/bin/clang++ -DNDEBUG  -O3 -DNDEBUG   -w -Werror=date-time --rocm-path=/opt/botworker/llvm/External/hip/rocm-6.3.0 --offload-arch=gfx908 --offload-arch=gfx90a --offload-arch=gfx1030 --offload-arch=gfx1100 -xhip -mfma -MD -MT External/HIP/CMakeFiles/TheNextWeek-hip-6.3.0.dir/workload/ray-tracing/TheNextWeek/main.cc.o -MF External/HIP/CMakeFiles/TheNextWeek-hip-6.3.0.dir/workload/ray-tracing/TheNextWeek/main.cc.o.d -o External/HIP/CMakeFiles/TheNextWeek-hip-6.3.0.dir/workload/ray-tracing/TheNextWeek/main.cc.o -c /home/botworker/bbot/clang-hip-vega20/llvm-test-suite/External/HIP/workload/ray-tracing/TheNextWeek/main.cc
fatal error: error in backend: Cannot select: intrinsic %llvm.amdgcn.readfirstlane
clang++: error: clang frontend command failed with exit code 70 (use -v to see invocation)
clang version 22.0.0git (https://github.com/llvm/llvm-project.git 907b7d0f07bb72a4a9732e234621adb589f77d42)
Target: x86_64-unknown-linux-gnu
```

https://github.com/llvm/llvm-project/pull/145859