asan: heap buffer overflow in _bfd_error_handler

asan: heap buffer overflow in _bfd_error_handler

On coff_slurp_symbol_table printing "unrecognized storage class"
for a symbol error.  If the symbol name is the last string in its
section and not terminated, we run off the end of the buffer.

	* coffgen.c (build_debug_section): Terminate the section with
	an extra 0.