[v3] add -fno-exceptions support

[Benjamin Kosnik]

> It sounds like libsupc++ only needs the macros
> (try/catch/__throw_exception_again) from that header, right?

Right. So, just move the header into libsupc++? Or just define the same 
macro bits in those files? Probably moving the header into libsupc++ is 
better.

Or we could just have a header with those defines, and have it be in 
libsupc++ and functexcept.h could include that header.  That might be best.

> They're in the EH document, which is separate.  A bit confusing, yes.

Kay. Thanks for clarifying. I'll have a look at that.

> > If __cxa_bad_cast/__cxa_bad_typeid are required for the ABI, and I'm
> > wrong, can't we just extend to __cxa_out_of_range etc and have all
> > this stuff in one place?
> 
> I'd really rather not--again, libsupc++ provides the library for a
> freestanding implementation.  This means clause 18 and any other hooks that
> the compiler might call from generated code.
> 
> Anything which does not fall under that description does not belong in
> libsupc++.
> 
> It's important to me that libsupc++ remain distinct from the rest of
> libstdc++, so that a program that only uses clause 18 can just link with
> libsupc++.

Ugh. Ok. I guess I'll figure out a way to consolidate this as per your 
original email then.

I see your point. This seems like a pretty shifty line that's being 
drawn, (18/19) but ok, whatever, let's get this in. It's a flaw (IMHO) in 
the standard but at least there is some kind of cogent rationale for the 
implementation. 

thanks for the quick reply,
benjamin