optimize reserved type check

vlib/compiler/for.v

@@ -22,6 +22,7 @@ fn (p mut Parser) for_st() {
 	else if next_tok == .decl_assign || next_tok == .assign || p.tok == .semicolon {
 		p.genln('for (')
 		if next_tok == .decl_assign {
+			p.check_not_reserved()
 			p.var_decl()
 		}
 		else if p.tok != .semicolon {

vlib/compiler/parser.v

@@ -697,7 +697,7 @@ fn (p mut Parser) check_string() string {
 }
 
 fn (p mut Parser) check_not_reserved () {
-	if p.lit in Reserved_Types {
+	if Reserved_Types[p.lit] { 
 		p.error('`$p.lit` can\'t be used as name') 
 	}
 }