adb: add support for O_CLOEXEC to unique_fd pipe wrapper.

using unique_fd = android::base::unique_fd_impl<AdbCloser>;

#if !defined(_WIN32)

inline bool Pipe(unique_fd* read, unique_fd* write) {

inline bool Pipe(unique_fd* read, unique_fd* write, int flags = 0) {

    int pipefd[2];

    if (pipe(pipefd) != 0) {

    if (pipe2(pipefd, flags) != 0) {

        return false;

    }

    read->reset(pipefd[0]);