llvm build fix

[allcreater]

No description provided.

[Copilot]

Pull request overview

Updates the project’s CMake configuration and CI setup to better support C++23 builds (including module/std import experimentation) across platforms.

Changes:

• Centralized common CMake preset settings (Ninja generator + build/install directories) into the shared base preset.
• Tightened C++ standard enforcement and updated the CMake version gating for CMAKE_EXPERIMENTAL_CXX_IMPORT_STD.
• Adjusted Ubuntu CI compiler setup toward LLVM/Clang 19 and attempted to force clang/clang++ to point to version 19.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
CMakePresets.json	Moves generator/build/install directory settings into the shared base preset for reuse.
CMakeLists.txt	Enforces C++23 more strictly and updates experimental import std GUID selection by CMake version.
.github/workflows/cmake-multi-platform.yml	Updates Ubuntu compiler setup to LLVM/Clang 19 and adds update-alternatives steps.

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[Copilot]

The new update-alternatives calls assume /usr/bin/clang-19 and /usr/bin/clang++-19 exist on the runner. If aminya/setup-cpp installs LLVM into a different prefix (common on GitHub runners), this step will fail and break CI. Consider either (a) installing clang-19 via apt-get explicitly before calling update-alternatives, (b) guarding these commands with an existence check, or (c) setting CC/CXX to the exact compiler path provided by the setup action instead of rewriting system alternatives.

Suggested change

	sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-19 100
	sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-19 100
	if [ -x /usr/bin/clang-19 ]; then
	sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-19 100
	fi
	if [ -x /usr/bin/clang++-19 ]; then
	sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-19 100
	fi