[compiler-rt] Adding Separate OpenMP Offloading Backend to `libcxx/include/__algorithm/pstl_backends` (PR #66968)

[Anton Rydahl via llvm-commits]

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@@ -807,6 +815,11 @@ else()
                        Valid backends are: serial, std_thread and libdispatch")
 endif()
 
+config_define_if(LIBCXX_ENABLE_GPU_OFFLOAD _LIBCPP_PSTL_GPU_OFFLOAD)
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AntonRydahl wrote:

I have tried to restructure the CMake file as sugegsted. However, I had issues with making a configuration variable that could be overridden. Do you know what type of cache should be used in `set(LIBCXX_PSTL_BACKEND ...)` to allow users to override it? 

https://github.com/llvm/llvm-project/pull/66968