FLTK detection in configure

[Paul Boven]

Hi everyone,

The FLTK backend to Octave seems quite interesting, so I've been trying 
to build an FLTK enabled version from the current hg repo. I'm running 
into some issues trying to build this:

1. Configure detects fltk and fltk-config (version 1.1.10) fine, but 
fails on:

configure:32400: checking for OpenGL support in FLTK
configure:32423: gcc -c -g -O2 -pthread -g -O2 -D_THREAD_SAFE 
-D_REENTRANT  conftest.c >&5
In file included from /usr/include/FL/gl.h:38,
                 from conftest.c:500:
/usr/include/FL/Enumerations.H:187: error: expected '=', ',', ';', 'asm' 
or '__attribute__' before 'fl_define_FL_ROUND_UP_BOX'

(and a few hundred more errors). The main problem here is that 
/usr/include/FL/gl.h in turn includes a C++ header file 
(/usr/include/FL/Enumerations.H), so 'regular' gcc cannot compile it 
(thanks to Jordi for spotting this).

2. Surprisingly, configure then thinks the test succeeded:

configure:32434: result: yes

And config.h does indeed have "#define HAVE_FLTK 1"

So after running configure, there are no warnings that the FLTK backend 
will not be built.

The good news is that FLTK ends up being built and working. The only 
thing that is not working is the menu buttons at the top 
(File/Edit/Help) - but such buttons also do not work on the demo 
applications that come with FLTK such as flsudoku.

Regards, Paul Boven.