stdlib: import endian head file from freebsd

stdlib: import endian head file from freebsd

Import endian head files from FreeBSD 11.0. The link of FreeBSD source code
is https://github.com/freebsd/freebsd

Import machine/endian.h from sys/arm64/include/endian.h in FreeBSD.
commit d09ff72cef8e35dbf62f7363dcbf07b453f06243
Author: andrew <andrew@FreeBSD.org>
Date:   Mon Mar 23 11:54:56 2015 +0000

    Add the start of the arm64 machine headers. This is the subset needed to
    start getting userland libraries building.

    Reviewed by:        imp
    Sponsored by:       The FreeBSD Foundation

Import sys/endian.h from sys/sys/endian.h in FreeBSD.
commit 3c3fa2f5b0c7640373fcbcc3f667bf7794e8e609
Author: phk <phk@FreeBSD.org>
Date:   Thu May 20 06:16:13 2010 +0000

    Fix some way-past-brucification complaints from FlexeLint.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>