[vsipl++] compiler warnings

[Jules Bergmann]

Stefan Seefeld wrote:

> 
> 
> It appears I introduced these dummy return statements when doing the
> initial port to ghs. At the time, we were using --disable-exceptions,
> and with that option we would call 'fatal_exception()' instead of
> throwing an exception. As it happens that function is marked up
> as '__noreturn__', but the markup code was only visible if __GCC__ >= 2.
> 
> As it turns out, ghs understands GCC attributes, so this revised patch
> simply enables the VSIP_IMPL_NORETURN macro for ghs, too.
> 
> This means that now all three supported compilers (gcc, icc, ghs)
> recognize the __noreturn__ attribute, and thus no dummy return
> statement is needed any more.
> 
> The code is tested with gcc as well as ghs, both with and without
> --disable-exceptions.
> 

Looks good, please check this in. -- Jules