r230255 - Only lower __builtin_setjmp / __builtin_longjmp to

[Joerg Sonnenberger]

On Tue, Mar 03, 2015 at 04:00:58PM -0800, John McCall wrote:
> I think the best solution is for us to not claim to support __builtin_setjmp
> and __builtin_longjmp on targets that don't support them.  That way we
> avoid making any particular ABI commitment in the absence of an optimized
> implementation; even if you don't care about GCC compatibility, you should
> care about compatibility between clang versions.  And an error here would
> simply disable the feature in Ruby's configure check.

r231245 does this, we now bail out in the frontend if the backend is not
known to have support.

Joerg