add defer

compiler/ast/ast.odin

@@ -131,6 +131,8 @@ Stmt_Kind :: enum u8 {
 	For,
 	Break,
 	Continue,
+	Block,
+	Defer,
 }
 
 Assignment_Op :: enum u8 {
@@ -165,6 +167,9 @@ Stmt :: struct {
 	// `For` statements use `expr` as the iterable, `name` as the item capture,
 	// `index_name` as the optional index capture, and `pointer_capture` to
 	// distinguish `|@item|` from copy capture.
+	// `Block` statements (a bare `{ ... }` scope) use `body` as their statements.
+	// `Defer` statements use `update` as the deferred statement (which may itself
+	// be a `Block`).
 	captures:   []symbol.Id,
 	guard:      Expr_Id,
 	body:       []Stmt_Id,