Crash if function_end_locus not set

[Richard Kenner]

    While trying to compile the ada runtime in HEAD I tripped over a crash
    in annotate_with_file_line (called by lower_function_body via
    annotate_with_locus) because cfun->function_end_locus.file is NULL.
    Is this supposed to be always set?

I'm a little behind in check-ins.  Just set it to DECL_SOURCE_LOCATION
of current_function_decl for now.