[INFRA] Import NVIDIA/CCCL upstream as optimization reference library

CCCL (CUDA C++ Core Libraries) provides:
- CUB: device/block/warp-level GPU primitives (reduce, scan, sort, topk)
- Thrust: high-level parallel algorithms (transform_reduce, sort, scan)
- libcudacxx: CUDA C++ standard library (atomics, barriers, memory)
- cudax: experimental features (memory resources, allocators)
- Tuning policies: per-SM hardware-specific algorithm parameters

Competition optimization vectors mapped to CCCL:
- Output TPS (83% weight): warp_reduce, block_reduce, device_topk
- Input TPS (14% weight): device_scan, block_load, prefetch
- Cache TPS (3% weight): prefix caching strategy patterns
- Memory (0.9 util): pooled/cached/buddy allocators

Source: https://github.com/NVIDIA/cccl (shallow clone, HEAD only)
License: Apache-2.0

cccl_upstream/cudax/cmake/cudaxBuildCompilerTargets.cmake

@@ -0,0 +1,65 @@
+# Including this file defines the following targets:
+#
+# cudax.compiler_interface
+# - Interface target that includes all compiler settings for cudax tests, etc.
+
+cccl_get_cub()
+cccl_get_cudax()
+cccl_get_libcudacxx()
+cccl_get_thrust()
+
+set(cuda_compile_options)
+set(cxx_compile_options)
+set(cxx_compile_definitions)
+
+if ("MSVC" STREQUAL "${CMAKE_CXX_COMPILER_ID}")
+  # C4848: support for attribute 'msvc::no_unique_address' in C++17 and earlier is a vendor extension
+  append_option_if_available("/wd4848" cxx_compile_options)
+
+  # XXX Temporary hack for STF !
+  # C4267: conversion from 'meow' to 'purr', possible loss of data
+  append_option_if_available("/wd4267" cxx_compile_options)
+
+  # C4459 : declaration of 'identifier' hides global declaration
+  # We work around std::chrono::last which hides some internal "last" variable
+  append_option_if_available("/wd4459" cxx_compile_options)
+
+  # stf used getenv which is potentially unsafe but not in our context
+  list(APPEND cxx_compile_definitions "_CRT_SECURE_NO_WARNINGS")
+endif()
+
+if ("Clang" STREQUAL "${CMAKE_CXX_COMPILER_ID}")
+  # stf heavily uses host device lambdas which break on clang due to a warning about the implicitly
+  # deleted copy constructor
+  # TODO(bgruber): remove this when NVBug 4980157 is resolved
+  append_option_if_available("-Wno-deprecated-copy" cxx_compile_options)
+endif()
+
+list(APPEND cxx_compile_definitions CCCL_ENABLE_ASSERTIONS)
+
+# Some groups related experimental code is located directly in libcu++ and is guarded by
+# _CUDAX_ENABLE_GROUP_FEATURES_IN_LIBCUDACXX macro, otherwise it would lead to a lot of code duplication. We define this
+# macro for cudax code globally, to get access to get access to the code.
+#
+# Can be removed once groups are no longer experimental.
+list(APPEND cxx_compile_definitions _CUDAX_ENABLE_GROUP_FEATURES_IN_LIBCUDACXX)
+
+cccl_build_compiler_interface(
+  cudax.compiler_flags
+  "${cuda_compile_options}"
+  "${cxx_compile_options}"
+  "${cxx_compile_definitions}"
+)
+
+add_library(cudax.compiler_interface INTERFACE)
+target_link_libraries(
+  cudax.compiler_interface
+  INTERFACE
+    # order matters here, we need the cudax options to override the cccl options.
+    cccl.compiler_interface
+    cudax.compiler_flags
+    libcudacxx::libcudacxx
+    CUB::CUB
+    Thrust::Thrust
+    cudax::cudax
+)