[gfortran, fix PR 25097] Additional constraints on FORALL headers

[Paul Thomas]

Tobi,
>
>
> Built and testing on i386-darwin.  Ok, provided the testsuite passes?
>
OK - many thanks.

Paul

PS We have a number of functions that sweep through an expression and 
doing something by comparison with a symbol.  I have been meaning for a 
long time to put together a master function to do this - I'll likely do 
it when I finally get around to PR29389.