[REDACTED] decode_local_label_name sprintf into fixed obstack size

In [REDACTED], decode_local_label_name() builds an error-message string using sprintf() into memory obtained from obstack_alloc() sized only as strlen(message_format)+30. The allocation is not computed from the full formatted output size, so large label/instance numbers could overflow the allocated buffer, corrupting heap/stack (via obstack) memory.