[flang] Catch attempts to initialize allocatable components with DATA statement

[klausler]

Summary

Nice try, but no, you can't initialize an instance of a derived type using a
structure constructor that has a component corresponding to an allocatable
component.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Evaluate/initial-image.cpp

if (elements * elementBytes != bytes) {
         auto scalar{x.At(at)};
         // TODO: length type parameter values?
         for (const auto &[symbolRef, indExpr] : scalar) {
           const Symbol &component{*symbolRef};
           if (component.offset() + component.size() > elementBytes) {
             return SizeMismatch;
           } else if (IsPointer(component)) {
             AddPointer(offset + component.offset(), indExpr.value());
+          } else if (IsAllocatable(component) || IsAutomatic(component)) {
+            return NotAConstant;
           } else {
             Result added{Add(offset + component.offset(), component.size(),
                 indExpr.value(), context)};
             if (added != Ok) {
               return added;
             }
           }
         }

flang/test/Semantics/data01.f90

 ! RUN: %python %S/test_errors.py %s %flang_fc1
 !Test for checking data constraints, C882-C887
 module m1
   type person
     integer :: age
     character(len=25) :: name
   end type
   integer, parameter::digits(5) = ( /-11,-22,-33,44,55/ )
   integer ::notConstDigits(5)
   real, parameter::numbers(5) = ( /-11.11,-22.22,-33.33,44.44,55.55/ )
   integer, parameter :: repeat = -1
   integer :: myAge = 2
   type(person) associated
+  type hasAlloc
+    integer, allocatable :: a(:)
+  end type
 end
 
 subroutine CheckRepeat
   use m1
   type(person) myName(6)
   !C882
   !ERROR: Missing initialization for parameter 'uninitialized'
   integer, parameter :: uninitialized
subroutine CheckValue
   integer :: x, y, z
   !OK: constant array element
   data x / a(1) /
   !C886, C887
   !ERROR: DATA statement value 'a(int(i,kind=8))' for 'y' is not a constant
   data y / a(i) /
   !ERROR: DATA statement value 'b(1_8)' for 'z' is not a constant
   data z / b(1) /
+  type(hasAlloc) ha
+  !ERROR: DATA statement value 'hasalloc(a=0_4)' for 'ha' is not a constant
+  data ha / hasAlloc(0) /
 end