[committed] testsuite: solib-disc: Use `standard_output_file'

[Maciej W. Rozycki]

On Thu, 6 Oct 2016, Simon Marchi wrote:

> Did you consider using standard_testfile to define the usual testfile, srcfile
> and binfile?

 Nope, I've got too many commitments right now to make non-essential 
clean-ups.  Please feel free to try yourself.

  Maciej