[gtkada] Configure doesn't find openGL

[Roger Mc Murtrie]

As suggested by https://developer.apple.com/library/mac/qa/qa1613/_index.html, I tried
CC='/usr/bin/gcc -g -O0' LDFLAGS='-framework GLUT -framework OpenGL -framework Cocoa' ./configure --enable-build=Debug --with-GL=GL --disable-shared
but
configure responded with:
checking for OpenGL... no
checking for GL32... no
checking for Mesa... no
checking Mesa with pthreads... no
configure: error: Missing OpenGL library

/System/Library/Frameworks definitely has  GLUT, OpenGL and Cocoa.
Maybe some work needed on the configure script.
My main priority at the moment is just to try and get testgtk working withOpenGL under the current configuration.
If I can sort that out then I'll probably have a go at implementing your "best approach".

> On 6 Sep 2016, at 5:17 PM, Emmanuel Briot <briot at adacore.com> wrote:
> 
>> Else a new value GLQuartz or whatever should be added in configure with "-framework GLUT -framework OpenGL" instead of "-lGLU -lGL" for GTK built with Quartz.
>> See https://developer.apple.com/library/mac/qa/qa1613/_index.html.
> 
> That sounds like the best approach, I think. On OSX, we should not require people to use
> the X11 backend...