[flang][debug] Support assumed size arrays. (#96316)

Here we don't know the size of last dimension and use a null subrange
for that. User will have to provide the dimension when evaluating
variable of this type. The debugging looks like as follows:

subroutine fn(a1, a2)
 integer  a1(5, *), a2(*)
...
end

(gdb) p a1(1,2)
$2 = 2
(gdb) p a2(3)
$3 = 3
(gdb) ptype a1
type = integer (5,*)
(gdb) ptype a2
type = integer (*)

0 files changed, 0 insertions, 0 deletions