d: Fix failing test with 32-bit compiler [PR114434]

Since the introduction of gdc.test/runnable/test23514.d, it's exposed an
incorrect compilation when adding a 64-bit constant to a link-time
address.  The current cast to size_t causes a loss of precision, which
can result in incorrect compilation.

	PR d/114434

gcc/d/ChangeLog:

	* expr.cc (ExprVisitor::visit (PtrExp *)): Get the offset as a
	dinteger_t rather than a size_t.
	(ExprVisitor::visit (SymOffExp *)): Likewise.

gcc/d/expr.cc

@@ -1499,7 +1499,7 @@ class ExprVisitor : public Visitor
   void visit (PtrExp *e) final override
   {
     Type *tnext = NULL;
-    size_t offset;
+    dinteger_t offset;
     tree result;
 
     if (e->e1->op == EXP::add)
@@ -2074,7 +2074,7 @@ class ExprVisitor : public Visitor
   void visit (SymOffExp *e) final override
   {
     /* Build the address and offset of the symbol.  */
-    size_t soffset = e->isSymOffExp ()->offset;
+    dinteger_t soffset = e->isSymOffExp ()->offset;
     tree result = get_decl_tree (e->var);
     TREE_USED (result) = 1;