In custom configuration data, indicate which sources are associated with the active build target

Bug type: Language Service

Describe the bug

• Windows 10:
• Latest: 1.56
• C/C++ Extension Version: 1.4.0
• Other extensions you installed: CMake Tools (1.7.2)

A single C codebase that has 2 CMake targets/proejcts defined for it: One using CUDA and another not using it (plain C).
The same codebase is compiled to either of these depending on which target is current/active.
CUDA-related portions are within #ifdef __CUDACC__ blocks.
Compilation succeeds on both targets, producing working executables.
But the editing experience is not adjusting properly.
Switchin back and forth between targets doesn't inform the syntax highlighting and code anlysis of a CUDA target being enabled/disabled. It always just debahves as if the projects aren't using CUDA.
There is a .cu file who's #include is under an #ifdef __CUDACC__ block, and when opening it even while the CUDA target is active, none of the CUDA-specific syntax is considered properly, so is full of errors being reported visually - even though it compiles and runs just fine.

Steps to reproduce

1. Start a new CUDA CMake project'
2. Create a code.h file with a #ifdef __CUDACC__ block declaring a __constant__ variable.
3. Create a cuda_code.cu file and include it into code.h under that #ifdef __CUDACC__, and add some CUDA-specific code in it.
4. Include code.h in main.cu (Add #include code.h).
5. Duplicate main.cu and rename it's file extension to just .c
6. Duplicate the project definition in the CMakeLists.txt file, renaming it to something else and making it a non-CUDA target/project (remove the CUDA term in the project() directive, as well as any target properties such as CUDA_SEPARABLE_COMPILATION), then change it's target executable to be main.c insteaf of main.cu.
7. After CMake reconfigures, select the CUDA-enabled target as the active one, and open cuda_code.cu - see how the syntax highlighting isn't working. Also open code.h and see how the #ifdef __CUDACC__ block is greyed out.

Expected behavior
The code analysis and syntax highlighting should get enabled and disabled appropriately when switchin between the CUDA vs. the non-CUDA targets.
Note: See attached animated-gif

Code sample and logs

#ifdef __CUDACC__
    #ifndef NDEBUG
        #define gpuErrchk(ans) { gpuAssert((ans), __FILE__, __LINE__); }
        inline void gpuAssert(cudaError_t code, const char *file, int line, bool abort=true) {
            if (code != cudaSuccess) {
                fprintf(stderr,"GPUassert: %s %s %d\n", cudaGetErrorString(code), file, line);
                if (abort) exit(code);
            }
        }
    #else
        #define gpuErrchk(ans) ans
    #endif
#endif

• Configurations in c_cpp_properties.json
  None (default)

• Logs from running C/C++: Log Diagnostics from the VS Code command palette
  Nothing special:

-------- Diagnostics - 5/12/2021, 7:11:28 PM
Version: 1.4.0-insiders
Current Configuration:
{
    "name": "Win32",
    "includePath": [
        "${workspaceFolder}/**"
    ],
    "defines": [
        "_DEBUG",
        "UNICODE",
        "_UNICODE"
    ],
    "windowsSdkVersion": "10.0.19041.0",
    "compilerPath": "C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.28.29910/bin/Hostx64/x64/cl.exe",
    "cStandard": "c17",
    "cppStandard": "c++17",
    "intelliSenseMode": "windows-msvc-x64",
    "configurationProvider": "ms-vscode.cmake-tools",
    "compilerArgs": [],
    "intelliSenseModeIsExplicit": true,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "compilerPathIsExplicit": true,
    "browse": {
        "path": [
            "${workspaceFolder}/**"
        ],
        "limitSymbolsToIncludedHeaders": true
    }
}
Custom browse configuration: 
{
    "browsePath": [
        "d:/code/c/raytracerxpu"
    ],
    "standard": "c++14",
    "compilerPath": "c:/program files (x86)/microsoft visual studio/2019/community/vc/tools/llvm/x64/bin/clang-cl.exe",
    "compilerArgs": [
        "-D_WINDOWS",
        "-Xcompiler=\" /GR /EHsc\"",
        "-Xcompiler=\"-O2 -Ob2\"",
        "-DNDEBUG",
        "--generate-code=arch=compute_52,code=[compute_52,sm_52]",
        "-Xcompiler=-MD",
        "-std=c++14"
    ]
}
Custom configurations:
[ D:\Code\C\RayTracerXPU\main.c ]
{
    "defines": [
        "WIN32",
        "_WINDOWS",
        "NDEBUG"
    ],
    "includePath": [],
    "compilerPath": "c:/program files (x86)/microsoft visual studio/2019/community/vc/tools/llvm/x64/bin/clang-cl.exe",
    "compilerArgs": [
        "/DWIN32",
        "/D_WINDOWS",
        "/O2",
        "/Ob2",
        "/DNDEBUG",
        "-MD"
    ]
}
Translation Unit Mappings:
[ D:\Code\C\RayTracerXPU\main.c ]:
    D:\CODE\C\RAYTRACERXPU\LIB\RENDER\RAYTRACER.H
    D:\CODE\C\RAYTRACERXPU\LIB\CORE\TYPES.H
Translation Unit Configurations:
[ D:\Code\C\RayTracerXPU\main.c ]:
    Process ID: 4504
    Memory Usage: 64 MB
    Compiler Path: c:/program files (x86)/microsoft visual studio/2019/community/vc/tools/llvm/x64/bin/clang-cl.exe
    Includes:
        C:\PROGRAM FILES (X86)\MICROSOFT VISUAL STUDIO\2019\COMMUNITY\VC\TOOLS\LLVM\X64\LIB\CLANG\11.0.0\INCLUDE
        C:\PROGRAM FILES (X86)\MICROSOFT VISUAL STUDIO\2019\COMMUNITY\VC\TOOLS\MSVC\14.28.29910\INCLUDE
        C:\PROGRAM FILES (X86)\MICROSOFT VISUAL STUDIO\2019\COMMUNITY\VC\TOOLS\MSVC\14.28.29910\ATLMFC\INCLUDE
        C:\PROGRAM FILES (X86)\WINDOWS KITS\10\INCLUDE\10.0.19041.0\UCRT
        C:\PROGRAM FILES (X86)\WINDOWS KITS\10\INCLUDE\10.0.19041.0\SHARED
        C:\PROGRAM FILES (X86)\WINDOWS KITS\10\INCLUDE\10.0.19041.0\UM
        C:\PROGRAM FILES (X86)\WINDOWS KITS\10\INCLUDE\10.0.19041.0\WINRT
    Defines:
        WIN32
        _WINDOWS
        NDEBUG
        WIN32
        _WINDOWS
        NDEBUG
    Standard Version: c17
    IntelliSense Mode: windows-clang-x64
    Other Flags:
        --ms_compatibility
        --microsoft_version=1929
        --ms_extensions
        --clang
        --clang_version=110000
Total Memory Usage: 64 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 4161

Screenshots

Additional context
I've also tried different settings (without success) such as:

    "C_Cpp.intelliSenseEngine": "Tag Parser",
    "C_Cpp.default.intelliSenseMode": "windows-clang-x64",
    "C_Cpp.default.configurationProvider": "ms-vscode.cmake-tools",

Setting to "Tag Parser" has the opposite effect: CUDA syntax seems to always be on, even when the non-CUDA project is active.

Reproduce the two-target setup described in CMakeLists.txt, using the CMake Tools configuration provider and the C/C++ Log Diagnostics output as the first inspection points. Compare the active CUDA and non-CUDA target configurations while opening code.h and cuda_code.cu. Done means IntelliSense, syntax highlighting, and conditional code display follow the selected build target.