bug#24460: a workaround for Emacs-25.1.1 configure error on Mac 10.11.6 :AppKit.h usability no bur presence yes with gcc

[fu7mu4]

Hello emacs developers.

I'm fu7m4, one of Emacs user.

A configure Warning asks me to report this to all.

  ## Report this to bug-gnu-emacs@gnu.org ##

This warning/error's workaround may be wrong.

But my emacs 25.1 seems to be work well.

Thanks.

# Short Description

installing emacs 25.1 on Mac from source (nextstep build), the configure script with "--without-x" argument says that AppKit.h is found but not unusable ;

./configure --without-x

....snip....

checking AppKit/AppKit.h usability... no
checking AppKit/AppKit.h presence... yes
configure: WARNING: AppKit/AppKit.h: present but cannot be compiled
configure: WARNING: AppKit/AppKit.h:     check for missing prerequisite headers?
configure: WARNING: AppKit/AppKit.h: see the Autoconf documentation
configure: WARNING: AppKit/AppKit.h:     section "Present But Cannot Be Compiled"
configure: WARNING: AppKit/AppKit.h: proceeding with the compiler's result
configure: WARNING:     ## ------------------------------------ ##
configure: WARNING:     ## Report this to bug-gnu-emacs@gnu.org ##
configure: WARNING:     ## ------------------------------------ ##
checking for AppKit/AppKit.h... no
configure: error: The include files (AppKit/AppKit.h etc) that
are required for a Nextstep build are missing or cannot be compiled.
Either fix this, or re-configure with the option '--without-ns'.

#Environment

Mac :10.11.6

default compiler: gcc (MacPorts gcc5 5.4.0_0) 5.4.0

#Source

ftp mirror's source

#Steps for reproduce

curl -OL http://ftp.jaist.ac.jp/pub/GNU/emacs/emacs-25.1.tar.xz
tar Jxvf emacs-25.1.tar.xz
cd emacs-25.1
./configure --without-x

#Workaround

use clang instead of gcc, like:

CC=/usr/bin/clang ./configure --without-x