Dear all,

the attached patch fixes an ICE on invalid (non-integer)
specification expressions for character length in function
declarations.  It appears that the error handling was
already in place (mostly) and we need to essentially
prevent run-on errors.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

The PR is marked as a 10/11/12/13 regression, so I would
like to backport this as far as it seems reasonable.

Thanks,
Harald