I want to add this library to my existing C++ project, which I have included by adding it as a submodule in an external folder, where external/CMakeLists.txt is:

set(FMI4C_BUILD_SHARED FALSE)
add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/fmi4c)
set_target_properties(fmi4c PROPERTIES LINKER_LANGUAGE C)

When I try to build my project with the Visual Studio 17 2022 generator, it compiles fine, but when I use the Ninja generator the build fails. For reference this is my CMakePresets.json:

{
    "version": 2,
    "configurePresets": [
        {
            "name": "debug_windows",
            "displayName": "Debug Windows",
            "binaryDir": "${sourceDir}/build",
            "generator": "Visual Studio 17 2022",
            "cacheVariables": {
                "CMAKE_BUILD_TYPE": "Debug",
                "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
                "CMAKE_TOOLCHAIN_FILE": {
                    "value": "${sourceDir}/vcpkg/scripts/buildsystems/vcpkg.cmake",
                    "type": "FILEPATH"
                },
                "VCPKG_INSTALLED_DIR": "../../vcpkg_installed",
                "NEMO_BUILD_TESTS": "TRUE",
                "NEMO_BUILD_PYTHON_EXTENSION": "FALSE",
                "NEMO_BUILD_CPPTESTS": "TRUE"
            }
        },
        {
            "name": "release_windows",
            "displayName": "Release Windows",
            "binaryDir": "${sourceDir}/build",
            "generator": "Visual Studio 17 2022",
            "cacheVariables": {
                "CMAKE_BUILD_TYPE": "Release",
                "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
                "CMAKE_TOOLCHAIN_FILE": {
                    "value": "${sourceDir}/vcpkg/scripts/buildsystems/vcpkg.cmake",
                    "type": "FILEPATH"
                },
                "VCPKG_INSTALLED_DIR": "../../vcpkg_installed",
                "NEMO_BUILD_TESTS": "TRUE",
                "NEMO_BUILD_PYTHON_EXTENSION": "FALSE",
                "NEMO_BUILD_CPPTESTS": "TRUE"
            }
        },
        {
            "name": "debug_linux",
            "displayName": "Debug Linux",
            "binaryDir": "${sourceDir}/build",
            "generator": "Ninja",
            "cacheVariables": {
                "CMAKE_BUILD_TYPE": "Debug",
                "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
                "CMAKE_TOOLCHAIN_FILE": {
                    "value": "${sourceDir}/vcpkg/scripts/buildsystems/vcpkg.cmake",
                    "type": "FILEPATH"
                },
                "VCPKG_INSTALLED_DIR": "../../vcpkg_installed",
                "NEMO_BUILD_TESTS": "TRUE",
                "NEMO_BUILD_PYTHON_EXTENSION": "FALSE",
                "NEMO_BUILD_CPPTESTS": "TRUE"
            }
        },
        {
            "name": "release_linux",
            "displayName": "Release Linux",
            "binaryDir": "${sourceDir}/build",
            "generator": "Ninja",
            "cacheVariables": {
                "CMAKE_BUILD_TYPE": "Release",
                "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
                "CMAKE_TOOLCHAIN_FILE": {
                    "value": "${sourceDir}/vcpkg/scripts/buildsystems/vcpkg.cmake",
                    "type": "FILEPATH"
                },
                "VCPKG_INSTALLED_DIR": "../../vcpkg_installed",
                "NEMO_BUILD_TESTS": "TRUE",
                "NEMO_BUILD_PYTHON_EXTENSION": "FALSE",
                "NEMO_BUILD_CPPTESTS": "TRUE"
            }
        }
    ],
    "buildPresets": [

    ]
}

if I change the generator to Ninja for the windows builds, I get a lot of C1003 and C2440 errors, which I think is because the external library is being compiled using the C++ compiler instead of the C compiler

[build] C:Userstom.mcleansrcNemoexternalfmi4csrcfmi4c.c(4578): error C2440: '=': cannot convert from 'fmi3Status (__cdecl *)(fmi3Instance,const fmi3ValueReference *,size_t,fmi3Int8 *,size_t)' to 'fmi3GetInt8_t'
[build] C:Userstom.mcleansrcNemoexternalfmi4csrcfmi4c.c(4579): error C2440: '=': cannot convert from 'fmi3Status (__cdecl *)(fmi3Instance,const fmi3ValueReference *,size_t,fmi3UInt8 *,size_t)' to 'fmi3GetUInt8_t'
[build] C:Userstom.mcleansrcNemoexternalfmi4csrcfmi4c.c(4580): error C2440: '=': cannot convert from 'fmi3Status (__cdecl *)(fmi3Instance,const fmi3ValueReference *,size_t,fmi3Int16 *,size_t)' to 'fmi3GetInt16_t'
[build] C:Userstom.mcleansrcNemoexternalfmi4csrcfmi4c.c(4580): fatal error C1003: error count exceeds 100; stopping compilation

I am not sure why this is happening, I have tried to set the fmi4c library to be compiled with C by using

set_target_properties(fmi4c PROPERTIES LINKER_LANGUAGE C)

And have checked the CMakeLists.txt of fmi4c and at the top is has:

cmake_minimum_required(VERSION 3.15)
project(fmi4c C)
set(CMAKE_C_STANDARD 99)

How can I add this library to my existing c++ project with CMake?