how to debug 'extern' in c with vscode

I'm not familiar with c compiler,I know how to use gcc or g++ in terminal

I have

main.c

#include <stdio.h>

int count;
extern void write_extern();

int main()
{
   count = 5;
   write_extern();
}

support.c

#include <stdio.h>

extern int count;

void write_extern(void)
{
   printf("count is %d\n", count);
}

gcc main.c support.c

and the output file a.out works fine

but if I debug with vscode or code-runner plugin error shows

/"main Undefined symbols for architecture x86_64: "_write_extern", referenced from: _main in main-217186.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation)

my launch.json and task.json look like this:

"configurations": [
        {
            "name": "clang build and debug active file",
            "type": "cppdbg",
            "request": "launch",
            "program": "${fileDirname}/${fileBasenameNoExtension}",
            "args": [],
            "stopAtEntry": false,
            "cwd": "${workspaceFolder}",
            "environment": [],
            "externalConsole": false,
            "MIMode": "lldb",
            "preLaunchTask": "clang build active file"
        }
    ]

{
    "tasks": [
        {
            "type": "shell",
            "label": "clang build active file",
            "command": "/usr/bin/clang",
            "args": [
                "-g",
                "${file}",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ],
            "options": {
                "cwd": "/usr/bin"
            }
        }
    ],
    "version": "2.0.0"
}

how to config this?