MSVC IntelliSense stops working after wasi-sdk-15

MSVC C++ IntelliSense gets very confused with recent SDK versions. (Tested with Visual Studio 2019, 2022, and 2022 Preview builds.) Is this perhaps an upstream LLVM 14.0 issue?

(Variants of this issue appear in other MSVC projects that utilize wasi-sysroot but run through MSVC for IntelliSense.)

Steps to reproduce

1. Create empty directory

2. Download latest sysroot release (https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-21/wasi-sysroot-21.0.tar.gz)

3. Extract sysroot into [directory]\wasi-sysroot

4. Create test.cpp with the following contents:

    #include <string>
    
    int main() {
        std::string test("hello");
    }
   

5. Create CppProperties.json with the following contents:

   {
     "configurations": [
       {
         "name": "Repro",
         "includePath": [
           "${workspaceRoot}\\wasi-sysroot\\include",
           "${workspaceRoot}\\wasi-sysroot\\include\\c++\\v1",
           "${env.INCLUDE}"
         ],
         "intelliSenseMode": "windows-msvc-x64"
       }
     ]
   }
   

6. Open Visual Studio > File > Open Folder > [folder path]

7. Observe (after a bit of waiting), Visual Studio shows red squiggles™️on std::string usage

   

8. Close Visual Studio

9. Delete [folder]\.vs

10. Edit CppProperties.json and change intelliSenseMode to windows-clang-x64

11. Open Visual Studio > File > Open Folder > [folder path]

12. Observe (after a bit of waiting), Visual Studio shows no squiggles™️

    

Start with the provided test.cpp and CppProperties.json reproduction using the wasi-sysroot-21 release in Visual Studio. Compare windows-msvc-x64 and windows-clang-x64 IntelliSense behavior, then determine whether the issue is in the SDK/sysroot or upstream LLVM/MSVC before defining a fix and regression test.