use C style comments instead of C++ style comments

According to CONTRIBUTING.md,

Don't use C++ style comments

 /* This is the prefered comment style */

Use C++ style comments only for temporary comment e.g. commenting out some code lines.

src/codegen.c

@@ -535,15 +535,15 @@ for_body(codegen_scope *s, node *tree)
   node *n2;
   mrb_code c;
 
-  // generate receiver
+  /* generate receiver */
   codegen(s, tree->cdr->car, VAL);
-  // generate loop-block
+  /* generate loop-block */
   s = scope_new(s->mrb, s, tree->car);
 
   lp = loop_push(s, LOOP_FOR);
   lp->pc1 = new_label(s);
 
-  // generate loop variable
+  /* generate loop variable */
   n2 = tree->car;
   if (n2->car && !n2->car->cdr && !n2->cdr) {
     genop(s, MKOP_Ax(OP_ENTER, 0x40000));
@@ -718,7 +718,7 @@ gen_values(codegen_scope *s, node *t, int val)
   int is_splat;
 
   while (t) {
-    is_splat = (intptr_t)t->car->car == NODE_SPLAT; // splat mode
+    is_splat = (intptr_t)t->car->car == NODE_SPLAT; /* splat mode */
     if (n >= 127 || is_splat) {
       if (val) {
         pop_n(n);
@@ -756,7 +756,7 @@ gen_values(codegen_scope *s, node *t, int val)
       }
       return -1;
     }
-    // normal (no splat) mode
+    /* normal (no splat) mode */
     codegen(s, t->car, val);
     n++;
     t = t->cdr;
@@ -1531,7 +1531,7 @@ codegen(codegen_scope *s, node *tree, int val)
       int rhs = cursp();
 
       if ((intptr_t)t->car == NODE_ARRAY && nosplat(t->cdr)) {
-        // fixed rhs
+        /* fixed rhs */
         t = t->cdr;
         while (t) {
           codegen(s, t->car, VAL);
@@ -1580,7 +1580,7 @@ codegen(codegen_scope *s, node *tree, int val)
         }
       }
       else {
-        // variable rhs
+        /* variable rhs */
         codegen(s, t, VAL);
         gen_vmassignment(s, tree->car, rhs, val);
       }
@@ -1913,7 +1913,7 @@ codegen(codegen_scope *s, node *tree, int val)
     break;
 
   case NODE_ARG:
-    // should not happen
+    /* should not happen */
     break;
 
   case NODE_BLOCK_ARG:
@@ -2444,7 +2444,7 @@ scope_new(mrb_state *mrb, codegen_scope *prev, node *lv)
   }
   p->lineno = prev->lineno;
 
-  // debug setting
+  /* debug setting */
   p->debug_start_pos = 0;
   if(p->filename) {
     mrb_debug_info_alloc(mrb, p->irep);
@@ -2921,7 +2921,7 @@ mrb_generate_code(mrb_state *mrb, parser_state *p)
   scope->filename = p->filename;
   scope->filename_index = p->current_filename_index;
   if (setjmp(scope->jmp) == 0) {
-    // prepare irep
+    /* prepare irep */
     codegen(scope, p->tree, NOVAL);
     proc = mrb_proc_new(mrb, scope->irep);
     mrb_irep_decref(mrb, scope->irep);