Use C-style comments for C89 / ANSI C compatibility
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index e0efebf..bd94ffb 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -10495,7 +10495,7 @@
         static Py_ssize_t buffer_sizes[] = { 256, XATTR_LIST_MAX, 0 };
         Py_ssize_t buffer_size = buffer_sizes[i];
         if (!buffer_size) {
-            // ERANGE
+            /* ERANGE */
             path_error("listxattr", &path);
             break;
         }