[gfortran, patch] fix runtime out-of-bounds checking

[FX Coudert]

ping

> Today, as part of my bounds-checking series, here is a patch that
> fixes runtime bounds-checking. Currently, the front-end generates
> errors for valid code (for example, for zero-sized sections), which
> this patch corrects. I also added a check for zero-stride, and checks
> for the last element of sections. I also fixed the text of the
> messages, from "bounds mismatch" to "Array reference out of bounds".
>
> In fact, this patch generates code for the same checks than my
> previous patch for compile-time checks did.
>
> Bootstrapped and regtested on i686-linux, tested that it didn't
> introduce regressions for the testcase run with -fbounds-check. I also
> manually checked that runtime errors are obtained on all the erroneous
> statements of my compile-time testcase
> (http://gcc.gnu.org/ml/fortran/2006-06/msg00071.html).
>
> OK for mainline and 4.1?