[v3] add -fno-exceptions support

[Benjamin Kosnik]

> > 	* libsupc++/new_op.cc (new): Include functexcept.h. Use
> > 	std::__throw_bad_alloc() instead of throw bad_alloc.
> 
> This is wrong.  Nothing in libsupc++ should depend on anything but
> libsupc++, libgcc and (as little as possible) the C library.  Similarly,
> std::__throw_bad_cast should call __cxa_bad_cast, not the other way around.

Hmm. Maybe I should just move the functexcept.h/functexcept.cc bits into 
libsupc++. 

While I'm at it I should probably clean up libsupc++ WRT the new abi. I 
was trying to keep some of this stuff separated out though.

-benjamin