Fix: create a separate scope for the for loop clauses and body

Author: yui-915

src/b.rs

@@ -790,6 +790,7 @@ pub unsafe fn compile_statement(l: *mut Lexer, c: *mut Compiler) -> Option<()> {
             Some(())
         }
         Token::For => {
+            scope_push(&mut (*c).vars);
             get_and_expect_token(l, Token::OParen)?;
 
             let cond_label = allocate_label_index(c);
@@ -843,6 +844,7 @@ pub unsafe fn compile_statement(l: *mut Lexer, c: *mut Compiler) -> Option<()> {
             push_opcode(Op::JmpLabel{label: iter_label}, (*l).loc, c);
             push_opcode(Op::Label {label: out_label}, (*l).loc, c);
 
+            scope_pop(&mut (*c).vars);
             Some(())
         }
         Token::Return => {

tests/for_loop.b

@@ -1,5 +1,7 @@
 main() {
+  auto i; i = 69;
   for (auto i = 0; i < 3; i++) printf("i: %lld\n", i);
+  printf("i outside: %lld\n", i);
 
   auto j;
   for (j = 3; j < 9; j += 2) printf("j: %lld\n", j);