Re: fltk build and doc access problems

Neither.
You have the wrong define (ie. compiler option) set.  These are all those
-DNAME_IN_UPCASE options you see in the compile line.
You probably need to set the define as I showed for it to compile (or remove it
if it is already being defined).
The configure/extconf.rb script either does not check for what fltk version you
have or is broken in detecting it correctly and places the wrong options into
the makefile.
Part of this is perhaps because fltk1.xxx is slowly migrating into becoming
fltk2 and as part of adding some functionality some functions are changing
signature.  Thus, the need for ruby-fltk to have #ifdef optional compilations.

>
>Won't this cause the actual call to break?

Perhaps, but not likely.
Certainly not from the message you got (as I ran into it when compiling it
myself).

You are trying to call a function with a different number of parameters (in
C++, you can have several functions named the same way but considered different
by the number and types of parameters they take... thus called polymorphic
functions).  
On the error, the compiler shows you what other functions with the same name
(but other parameters) are available (ie. gives you a hint: saying... perhaps
you wanted to call one of these?).
If you compare the line of the error in the ruby-fltk source code, you will see
something like:

#if (defined(HAVE_SOME_CONSTANT))
  ... some code...
#else
.... some alternative code...
#endif

Check the number of parameters your call is complaining about and you will know
which code is being executed.   Define or undefine the appropiate constant to
use the other one.
The calls that changed are actually pretty trivial and ruby-fltk is coded to
take care of them already.