[llvm] [docs][CMake] Add CMakePreset, improve VS documentation (PR #84760)

[James Henderson via llvm-commits]

================
@@ -119,7 +120,55 @@ These instruction were tested with Visual Studio 2019 and Python 3.9.6:
  Select the last link: ``Source code (zip)`` and unpack the downloaded file using
  Windows Explorer built-in zip support or any other unzip tool.
 
-12. Finally, configure LLVM using CMake:
+12. Open the LLVM folder in Visual Studio or generate a solution via CMake.
+
+  At this point you can select if you want to use the
+  :ref:`native support for CMake<vs_native_cmake>` in Visual Studio or
+  :ref:`generate Visual Studio<gen_vs_cmake>` solution file from CMake.
+  Both integrations are supported in the LLVM project.
+
+.. _vs_native_cmake:
+
+Visual Studio native CMake support
+==================================
+
+Support for native CMake integration was added in Visual Studio 2019, but it has
+been made more robust in 2022. If you are using Visual Studio before 2022, it's
+recommended to generate a Visual Studio solution from CMake instead of using the
+native CMake integration.
+
+If you want to generate a Visual Studio Solution for older versions of Visual
+Studio or because that is a workflow that suits you better, please refer to the
+chapter below on :ref:generating Visual Studio Solution<gen_vs_cmake>.
+
+To use the native CMake support, launch Visual Studio 2022 and select the option
+Open a Local Folder and open the root llvm-project folder. This will
+automatically launch CMake (have some patience, it can be a bit slow) and
+populate the interface.
+
+LLVM ships with a default CMakePresets.json that is supposed to make it easy to
+get started, but usually you need to modify the settings used. The best way to
+do this is to create a CMakeUserPresets.json in the llvm subfolder and add your
+configuration there. For more information about the Preset system, see
+Microsoft's documentation
+<https://learn.microsoft.com/en-us/cpp/build/cmake-presets-json-reference>_.
+
+The default CMakePreset comes with MSVC and Clang targets. To use the Clang
+target, you need to have the C++ Clang compiler for Windows component of Visual
+Studio installed.
+
+To debug Clang and other binaries within Visual Studio, see Microsoft's
+documentation
+<https://learn.microsoft.com/en-us/cpp/build/configure-cmake-debugging-sessions>_.
+
+
+.. _gen_vs_cmake:
+
+Generate Visual Studio Solution with CMake
+==========================================
+
+1.  After following the steps above you can generate a Visual Studio Solution by
----------------
jh7370 wrote:

Nit: I find the "above" phrasing here a little ambiguous. Obviously from reading with the full context, this is referring to the points which end with getting the LLVM source, but if you jumped straight here, you might think "above" means the immediately previous section, i.e. using CMake within Visual Studio. Perhaps referring more specifically to the section might be best for clarity.

https://github.com/llvm/llvm-project/pull/84760