[flang] emit warning when encountering a non-variable actual argument when its corresponding dummy argument expects a VOLATILE variable
This patch implements @klausler's suggestion in `llvm-project` [issue #58973](https://github.com/llvm/llvm-project/issues/58973); encountering the `VOLATILE` attribute should produce a __warning__, not a __fatal error__.
When tested on the following Fortran program `snem0601_012_.f90`:
```fortran
module mod
contains
subroutine sub(m6,error)
integer,intent(inout) :: error
integer,volatile :: m6
if (any ((/m6/).ne.(/6/))) &
& then
error = 1
end if
end subroutine
end module
program fe1nvol12
use mod
integer :: error = 0
call sub(6,error)
if (error .ne. 0) then
print *,'NG: snem0601_012'
end if
print *,'pass: snem0601_012'
end program fe1nvol12
```
the following output is produced:
```bash
$ flang-new -fc1 snem0601_012_.f90
/noback/93u/Sandbox/issue_58973_volatile_dummy_arg/snem0601_012_.f90:21:12: warning: actual argument associated with VOLATILE dummy argument 'm6=' is not a variable
call sub(6,error)
^
```
Reviewed By: clementval, klausler
Differential Revision: https://reviews.llvm.org/D139134