feat(backend/riscv32): 实现基础的编译器功能

- 完成 RV32IMA 指令集的代码生成
- 添加整数运算、分支、调用等基本指令支持
- 实现从 IR 到机器码的转换
- 添加简单的测试用例和测试框架

ccompiler/frontend/lexer/token.c

@@ -30,14 +30,13 @@ void init_tokbuf(tok_buf_t *tokbuf, void *stream, get_tokbuf_func gettok) {
     tokbuf->cap = 0;
 }
 
-tok_t *peek_tok(tok_buf_t *tokbuf)
-{
+tok_t *peek_tok(tok_buf_t *tokbuf) {
     int idx = tokbuf->peek;
-    idx = ROUND_IDX(idx + 1);
+    tokbuf->peek = ROUND_IDX(idx + 1);
     if (tokbuf->size >= tokbuf->cap) {
         error("peek too deep, outof array size");
     }
-    if (tokbuf->peek == tokbuf->end) {
+    if (idx == tokbuf->end) {
         if (tokbuf->size == tokbuf->cap) {
             error("peek_tok buffer overflow");
         }
@@ -46,10 +45,9 @@ tok_t *peek_tok(tok_buf_t *tokbuf)
         }
         tokbuf->gettok(tokbuf->stream, &(tokbuf->buf[idx]));
         tokbuf->size++;
-        tokbuf->end = idx;
+        tokbuf->end = tokbuf->peek;
     }
-    
-    tokbuf->peek = idx;
+
     return &(tokbuf->buf[idx]);
 }