[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/libcudacxx/test/support/demangle.h

@@ -0,0 +1,51 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef SUPPORT_DEMANGLE_H
+#define SUPPORT_DEMANGLE_H
+
+#include <cstdlib>
+#include <string>
+
+#include "test_macros.h"
+
+#if !defined(TEST_HAS_NO_DEMANGLE)
+#  if defined(__GNUC__) || defined(__clang__)
+#    if __has_include("cxxabi.h") && !TEST_COMPILER(MSVC)
+#      include "cxxabi.h"
+#    else
+#      define TEST_HAS_NO_DEMANGLE
+#    endif
+#  else
+#    define TEST_HAS_NO_DEMANGLE
+#  endif
+#endif
+
+#if defined(TEST_HAS_NO_DEMANGLE)
+inline std::string demangle(const char* mangled_name)
+{
+  return mangled_name;
+}
+#else
+template <size_t N>
+struct Printer;
+inline std::string demangle(const char* mangled_name)
+{
+  int status = 0;
+  char* out  = __cxxabiv1::__cxa_demangle(mangled_name, nullptr, nullptr, &status);
+  if (out != nullptr)
+  {
+    std::string res(out);
+    std::free(out);
+    return res;
+  }
+  return mangled_name;
+}
+#endif
+
+#endif // SUPPORT_DEMANGLE_H