check_c_source_compiles("
#include <netdb.h>
int main(void) {
    struct protoent result;
    struct protoent *res = 0;
    char buf[1024];
    getprotobynumber_r(6, &result, buf, sizeof(buf), &res);
    return 0;
}
" SYSLOG_NG_HAVE_GETPROTOBYNUMBER_R)