[poppler] building 0.68 and 0.69

[Jason Crain]

On 2018-09-25, Valerio Messina <efa at iol.it> wrote:
> Building 0.67 work, so something changed in 0.68 generate this trouble.

Poppler switched from using its own cmake module to find OpenJPEG to
using the one that ships with cmake.