exception scheme checking

[Mark Mitchell]

Nathan Sidwell wrote:
> This patch fixes an issue I discovered in the exception scheme checking 
> of except.h.  It wasn't fully validating the consistency of the 
> sjlj/dwarf macros, leading to later confusing build failures.
> 
> The patch makes the errors more explicit, and adds a final double check 
> to catch any condition not previously diagnosed (as happens if one 
> naively tries to turn on dwarf-eh for pre-eabi arm).

OK.

-- 
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713