Update toolchain

[mingxwa]

Changes

• Updated Clang major version from 20 to 21. Added Clang 20 to compatibility tests.
• Updated GCC major version from 14 to 15 using GCC Docker container image.
• Updated NVHPC from 25.7 to 25.11.
• Updated dependencies to their latest versions:
  • fmt from 11.2.0 to 12.1.0. Also refactored proxy_fmt.h not to rely on fmt::is_char because it's removed in the latest 12.x.
  • google-benchmark from 1.9.0 to 1.9.4.
  • google-test from 1.15.2 to 1.17.0.
  • nlohmann-json from 3.11.3 to 3.12.0.

[Copilot]

Pull request overview

This pull request updates the project's toolchain and dependencies to their latest versions. The primary focus is upgrading major compiler versions (Clang 20→21, GCC 14→15, NVHPC 25.7→25.11) and core dependencies (fmt, google-test, google-benchmark, nlohmann-json). The PR also refactors proxy_fmt.h to maintain compatibility with fmt 12.x by replacing the removed fmt::is_char check with version-based type aliases.

• Updated three major compiler toolchains to their latest versions
• Upgraded four key dependencies to newer releases
• Refactored fmt integration code to use version-specific type aliases instead of removed API
• Consolidated FetchContent setup in parent CMakeLists.txt for better organization

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
.github/workflows/bvt-clang.yml	Updates Clang from version 20 to 21 in the main build and test workflow
.github/workflows/bvt-gcc.yml	Updates GCC from version 14 to 15 using Docker container approach
.github/workflows/bvt-nvhpc.yml	Updates NVHPC from version 25.7 to 25.11
.github/workflows/bvt-compatibility.yml	Adds Clang 20 to compatibility tests alongside existing compiler versions
CMakeLists.txt	Consolidates FetchContent setup and declares fmt 12.1.0 in parent CMake file
include/proxy/v4/proxy.h	Fixes whitespace formatting in macro definition
include/proxy/v4/proxy_fmt.h	Refactors to use version-based type aliases instead of removed fmt::is_char API
tests/proxy_fmt_format_tests.cpp	Removes NVCOMPILER pragma guards that are no longer needed
tests/CMakeLists.txt	Updates google-test to 1.17.0 and removes redundant FetchContent declarations
benchmarks/CMakeLists.txt	Updates google-benchmark to 1.9.4 and removes redundant FetchContent setup
docs/CMakeLists.txt	Removes redundant fmt FetchContent declaration now in parent CMake
tools/report_generator/CMakeLists.txt	Updates nlohmann-json to 3.12.0 with new archive URL
cmake/msft_proxy4ModuleTargets.cmake	Adds Clang compiler flag to suppress C++2b extension warnings

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