Function decorations for libsupc++

[Paolo Carlini]

Jan Hubicka wrote:
> Hi,
> this patch adds decorations to libsupc++.  I primarily wanted to decorate
> std::terminate. Adding the other decorations is not going to help aplications
> since all the stuff is hidden in the libsupc++ itself.  Doing so however
> saves 7KB from the library size and will hopefully let us to copmile these bits
> with warnings about missing flags enabled to make stuff easier to maintain.
>
> Tested od x86_64-linux, OK?
>   
Basically ok, but I say let's not waste time figuring out which header
can be included by the user code and which not, let's consistently use
everywhere __pure__, __const__, and __noreturn__. Ok with this trivial
change.

Paolo.