binutils opcodes/s390-mkopc.c: stack buffer overflow via strcpy/strcat into fixed 15-byte arrays

In opcodes/s390-mkopc.c, insertExpandedMnemonic() uses fixed-size stack buffers (prefix/suffix/number/new_mnemonic of size 15) and copies/concatenates unbounded substrings from the input mnemonic. It performs strcpy(new_mnemonic, prefix) and strcat() with prefix/suffix contents without enforcing that the resulting strings fit, enabling stack buffer overflow when mnemonics exceed expected length.