Ensure the format argument of RUBY_DEBUG_LOG is a string literal

vm_debug.h

@@ -94,18 +94,18 @@ bool ruby_debug_log_filter(const char *func_name);
 
 // convenient macro to log even if the USE_RUBY_DEBUG_LOG macro is not specified.
 // You can use this macro for temporary usage (you should not commit it).
-#define _RUBY_DEBUG_LOG(...) ruby_debug_log(__FILE__, __LINE__, __func__, __VA_ARGS__)
+#define _RUBY_DEBUG_LOG(...) ruby_debug_log(__FILE__, __LINE__, __func__, "" __VA_ARGS__)
 
 #if USE_RUBY_DEBUG_LOG
 
 #define RUBY_DEBUG_LOG(...) do { \
   if (ruby_debug_log_mode && ruby_debug_log_filter(__func__)) \
-    ruby_debug_log(__FILE__, __LINE__, __func__, __VA_ARGS__); \
+    ruby_debug_log(__FILE__, __LINE__, __func__, "" __VA_ARGS__); \
 } while (0)
 
 #define RUBY_DEBUG_LOG2(file, line, ...) do { \
   if (ruby_debug_log_mode && ruby_debug_log_filter(__func__)) \
-    ruby_debug_log(file, line, __func__, __VA_ARGS__); \
+    ruby_debug_log(file, line, __func__, "" __VA_ARGS__); \
 } while (0)
 
 #else