Ubuntu – VS Code C/C++ extension intellisense can't detect environment specific functions

When I’m writing C codes on VS Code, IntelliSense can’t detect functions declared in standard libraries, while the project compile properly.

Details:

The flockfile function is declared as void flockfile (FILE *__stream) in stdio.h, however IntelliSense treats the function wrongly.

I found the information that old C compilers treat undeclared functions as int functionname().
So I guess that intellisense thinks that flockfile hasn’t been declared yet, even though I certainly include stdio.h at the top of the file which uses flockfile.

When I opened stdio.h on VS Code, the definition of fnlockfile is displayed as the unreachable code.

However, the project compile properly without warnings related to fnlockfile and the built app also works properly.
So I think the root cause of this problem is that the compiler used by IntelliSense receives different arguments from ones the actual compiler receives.

How can I make IntelliSense interpret codes as well as the actual compiler does?

I searched around the related reports on the internet, but I wasn’t able to find.
Adding __USE_POSIX199506 definition before including stdio.h might address the issue, but I’m using stdio.h in a couple of files and I don’t want to write that definition every time I include stdio.h.

Environment:

Host OS: Windows10
Guest OS: Ubuntu 22.04.4 LTS (WSL2)
Compiler: gcc version 11.4.0 (Ubuntu 11.4.0-1ubuntu1~22.04)
Editor: VS Code(1.87.2) with C/C++ extension from Microsoft (v1.19.9)

.vscode/c_cpp_properties.json file;

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "defines": [],
            "compilerPath": "/usr/bin/gcc",
            "cStandard": "c17",
            "cppStandard": "gnu++17",
            "intelliSenseMode": "linux-gcc-x64",
            "configurationProvider": "ms-vscode.cpptools"
        }
    ],
    "version": 4
}

which gcc answers /usr/bin/gcc

I’m not savvy in compiler around things, so sorry if it was a silly question…

Edit (add minimap reproducible example)

1. Create a new project folder.

2. Create main.c

#include <stdio.h>

int main(void)
{
    flockfile(stderr);
    fprintf(stderr, "hello worldn");
    funlockfile(stderr);
    return 0;
}

3. Create .vscode folder and put the above c_cpp_properties.json.

4. Run below commands to build and run an executable.

$ cc -g -W -Wall -Wno-unused-parameter -iquote . -pthread -iquote platform/linux -c main.c -o main.o
$ cc -g -W -Wall -Wno-unused-parameter -o out.a main.o
$ ./out.a
hello world

4. However, IntelliSense in VS Code can’t detect flockfile properly.