CHECK_C_SOURCE_COMPILES("
 #define _GNU_SOURCE
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/socket.h>
 #include <fcntl.h>
 int main(int argc,const char *argv[]) {
    open(\".\",O_RDONLY | O_CLOEXEC);
    socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
    return 0;
 }" HAS_CLOEXEC_GNU_SOURCE)