[Patch, fortran] Fix PR19101 missing & in character continuation not caught

[Jerry DeLisle]

> 
> I looked at using gfc_error_now and it leads to segfaults due
> to freeing partially filled lines/namespaces/etc.  So, I looked
> at your gfc_warning_now suggestion.  This actually works with
> the caveat that in fixed form source a tab in column is reported
> different than how it is reported in gfc_warning_now.  I now
> have
> 

While away at work I was also giving this some thought and I think for the & 
continuation I would like to give a warning on -pedantic and otherwise try to 
complete the continuation at the first non whitespace character encountered. 
This is the least intrusive approach and the default behavior will match at 
least one other compiler.

I will give this a try and report back.  Thanks for good discussion.

Jerry