RFC: readelf: Explain why LLVM bitcode files cannot be read

[Nick Clifton]

Hi Richard,

> This fails to build on ubuntu (which defaults to -Werror=format-security):
> 
> /home/rearnsha/gnusrc/gcc-cross/master/binutils/readelf.c:5738:6: error: format not a string literal and no format arguments [-Werror=format-security]

Yeah - I noticed this 10 minutes after I committed the original patch.
I have since applied a small update which fixes the problem, so if
you update the sources, the error should go away.

Cheers
   Nick