Archive sanity checks

Adds some sanity checking to size values read from file.

	* archive.c (do_slurp_bsd_armap): Increase minimum parsed_size, and
	bfd_set_error on failing test.  Don't bother changing bfd_error on
	file read error.  Check symdef_count is multiple of BSD_SYMDEF_SIZE.
	Check sym name is within string buffer.  Use size_t for some vars.
	(do_slurp_coff_armap): Use size_t for some variables, fix size of
	int_buf.  Don't change bfd_error on file read error.  Use
	_bfd_mul_overflow when calculating carsym buffer size.  Reorder
	calculations to catch overflows before they occur.  malloc and
	free raw armap rather than using bfd_alloc.  Read raw armap before
	allocating carsym+strings buffer.
	(_bfd_slurp_extended_name_table): Localize variables.  Check
	name size against file size.