Using Clang kit, headers are not found for Intellisense, despite cmake-tools being set as the Configuration Provider

Brief Issue Summary

When switching to the "Clang 8.0.0 for MSVC with Visual Studio Tools 2019 (amd64)" kit, all standard headers fail to be found and create a bevy of squiggles and terrible advice about setting includePath, something that feels really wrong and unmaintable.

My Configuration Provider in cpptools is "vector-of-bool.cmake-tools" as per the instructions right there in their extension.

Cpptools' Windows SDK version setting is set to "10.0.18362.0", which is installed on my system.

Code was run from the x64 Developer Command line, to ensure all MSVC environment variables were properly set. This did not help.

Expected:

1. Switching to Clang kit should have no deleterious effect on Intellisense's ability to find standard headers, which are known to be the same on Windows (the ones that cl.exe uses) since clang does not have its own on Windows.
2. Intellisense should be able to find the Windows SDK headers, (without manually pasting in include paths.)

Apparent Behavior:

Switching to Clang kit makes Intellisense in cpptools unable to find standard headers.

Platform and Versions

• Operating System: Windows
• CMake Version: 3.15
• VSCode Version: 1.37.1 etc.
• CMake Tools Extension Version: 1.1.3
• Cpptools: 0.25.1
• Compiler/Toolchain: Clang 8.0.0.0 for MSVC with Visual Studio Tools 2019 (amd64) kit

No source file or test is named in the issue. Start by reproducing the failure with the listed Clang kit, CMake Tools 1.1.3, cpptools 0.25.1, and Windows SDK 10.0.18362.0, then trace the Configuration Provider integration. Done means switching kits preserves discovery of standard and Windows SDK headers without manually adding include paths.