fix vardecl initialization value to not use stack eval anymore but separate assignment

(this causes the optimized assignment code gen to be used instead)
but some programs now end up larger in output size

compilerAst/src/prog8/ast/statements/AstStatements.kt

@@ -41,6 +41,15 @@ sealed class Statement : Node {
         else
             null
     }
+
+    fun previousSibling(): Statement? {
+        val statements = (parent as? IStatementContainer)?.statements ?: return null
+        val previousIdx = statements.indexOfFirst { it===this } - 1
+        return if(previousIdx >= 0)
+            statements[previousIdx]
+        else
+            null
+    }
 }