fix pr21419

[Diego Novillo]

On September 25, 2005 08:36, Paolo Bonzini wrote:

> Â Â Â Â Â Â Â Â PR c/21419
> Â Â Â Â Â Â Â Â * gimplify.c (gimplify_asm_expr): Raise an error if an output
> is read-only.

OK, with the test cases from 21420.