mem_sec.c: portability fixup.
# include <sys/mman.h>
# if defined(OPENSSL_SYS_LINUX)
# include <sys/syscall.h>
+# if defined(SYS_mlock2)
# include <linux/mman.h>
# include <errno.h>
# endif
+# endif
# include <sys/param.h>
# include <sys/stat.h>
# include <fcntl.h>
