Fix type casts from initializer lists to arrays of unspecified size

regression/ansi-c/Initializer_cast2/main.c

@@ -0,0 +1,6 @@
+int main()
+{
+  int A[(sizeof((int[]){1, 2, 3})==3*sizeof(int))?1:-1];
+
+  return 0;
+}

regression/ansi-c/Initializer_cast2/test.desc

@@ -0,0 +1,7 @@
+CORE
+main.c
+
+^EXIT=0$
+^SIGNAL=0$
+--
+^CONVERSION ERROR$

src/ansi-c/c_typecheck_expr.cpp

@@ -1100,7 +1100,14 @@ void c_typecheck_baset::typecheck_expr_typecast(exprt &expr)
     // or an expression for a pointer or scalar.
     // We produce a compound_literal expression.
     exprt tmp(ID_compound_literal, expr.type());
-    tmp.move_to_operands(op);
+    tmp.copy_to_operands(op);
+
+    // handle the case of TYPE being an array with unspecified size
+    if(op.id()==ID_array &&
+       expr.type().id()==ID_array &&
+       to_array_type(expr.type()).size().is_nil())
+      tmp.type()=op.type();
+
     expr=tmp;
     expr.set(ID_C_lvalue, true); // these are l-values
     return;