bug#28571: 25.3; Compile error on macOS Sierra

[mituharu]

> Patch pushed to emacs-26.

???  The OP did not reply whether he installed the Command Line Tools.
I still think the failure is due to not installing them.

As for binary compatibility issue, futimens, futimesat, utimensat are not
the only such functions.
For example, mkostemp, fstatat, fdopendir, readlinkat, and faccessat are
available on macOS 10.12, but not on all older OS X versions that Emacs 26
supports.
If you want to build a binary on a new version so that it also runs on
older versions,
then you need to use config.status generated on the oldest version anyway.

                                     YAMAMOTO Mitsuharu
                                mituharu@math.s.chiba-u.ac.jp