[PATCH, libgfortran] Fix for PR24699, PR24700, PR24719]

[Jerry DeLisle]

Jerry DeLisle wrote:

> OK for mainline?   OK for 4.0 branch? (with some minor changes, there is no
> is_internal_unit() in 4.0 branch)
> 
Of Course, bootstrapped and regression tested on i686-pc-linux-gnu.

OK?