undefined reference to `concatf'

I have gone through similar questions and seen answers given, where given and none of those points me to what I am doing wrong. I keep getting undefined reference to 'concatf' while the function is properly defined in the header file.

concatf.c

#include "concatf.h"


/*
 * vscprintf:
 * MSVC implements this as _vscprintf, thus we just 'symlink' it here
 * GNU-C-compatible compilers do not implement this, thus we implement it here
 */
#ifdef _MSC_VER
#define vscprintf _vscprintf
#endif

#ifdef __GNUC__
int vscprintf(const char *format, va_list ap)
{
    va_list ap_copy;
    va_copy(ap_copy, ap);
    int retval = vsnprintf(NULL, 0, format, ap_copy);
    va_end(ap_copy);
    return retval;
}
#endif


int vasprintf(char **strp, const char *format, va_list ap)
{
    int len = vscprintf(format, ap);
    if (len == -1)
        return -1;
    char *str = (char*)malloc((size_t) len + 1);
    if (!str)
        return -1;
    int retval = vsnprintf(str, len + 1, format, ap);
    if (retval == -1) {
        free(str);
        return -1;
    }
    *strp = str;
    return retval;
}

int concatf(char **strp, const char *format, ...)
{
    va_list ap;
    va_start(ap, format);
    int retval = vasprintf(strp, format, ap);
    va_end(ap);
    return retval;
}

concatf.h

#ifndef CONCATF_H
#define CONCATF_H

#if defined(__GNUC__) && ! defined(_GNU_SOURCE)
#define _GNU_SOURCE /* needed for (v)asprintf, affects '#include <stdio.h>' */
#endif
#include <stdio.h>  /* needed for vsnprintf    */
#include <stdlib.h> /* needed for malloc, free */
#include <stdarg.h> /* needed for va_*         */

int concatf(char **strp, const char *format, ...);

#endif // CONCATF_H

build.c

#include "concatf.h"

#include <stdio.h>
#include <stdlib.h>

extern char _binary_script_php_start;
extern char _binary_script_php_end;

int main(int argc, char *argv[]) {
    // EXTRACT OUR RESOURCE OBJECT INTO /tmp/test.php
    char *p = &_binary_script_php_start;
    FILE *fp = fopen("/tmp/test.php","wb");
    while ( p != &_binary_script_php_end ) {
        fputc(*p++,fp);
    }
    fclose(fp);
    // NOW READ IN OUR STANDARD ARGUMENTS AND LAUNCH OUR COMMAND
    int i = 1;
    char *cmd = "php /tmp/test.php";
    char *s = NULL;
    // asprintf(&s, "%s",cmd);
    // for(i = 1; i < argc; i++) {
    //     asprintf(&s, "%s \"%s\"",s,argv[i]);
    // }
    // concatf("%s",cmd);
    // for(i = 1; i < argc; i++) {
    //     concatf("%s \"%s\"",s,argv[i]);
    // }
    concatf(&s, "%s",cmd);
    for(i = 1; i < argc; i++) {
        concatf(&s, "%s \"%s\"",s,argv[i]);
    }
    system(s);
    free(s);
    unlink("/tmp/test.php"); // comment me out for debugging if you want
}

These codes run on my environment but fail to run on the second windows environment and those of my colleagues, I can't seem to point why that is the case. To run it you will need a php file named script.php run ld -r -b binary script.php data.o to complie your php file and gcc build.c data.o -o runme to link the php file with the build function. You can find the sample project here https://github.com/Sammiiie/C_php_http.