Yet another out-of-memory fuzzed object

Yet another out-of-memory fuzzed object

Do I care about out of memory conditions triggered by fuzzers?  Not
much.  Your operating system ought to be able to handle it by killing
the memory hog.  Oh well, this one was an element of a coff-alpha
archive that said it was a little less that 2**64 in size.  The
coff-alpha compression scheme expands at most 8 times, so we can do
better in bfd_get_file_size.

	* bfdio.c (bfd_get_file_size): Assume elements in compressed
	archive can only expand a maximum of eight times.
	* coffgen.c (_bfd_coff_get_external_symbols): Sanity check
	size of symbol table agains file size.