[RFA] Avoid ubsan complaint in BFD

[Nick Clifton]

Hi Tom,

> bfd/ChangeLog
> 2018-07-20  Tom Tromey  <tom@tromey.com>
> 
> 	* elf.c (bfd_get_elf_phdrs): Don't call memcpy with size 0.

Approved, please apply.

I am sidestepping the debate on whether memcpy should handle a size of 0 or not ...

Cheers
  Nick