(Fixes #1398) Add missing #include <cstdio> prior to jpeglib.h

This include is required prior to include jpeglib.h, as libjpeg-turbo explicitly does not include it as part of a libjpeg design constraint.

See https://github.com/libjpeg-turbo/libjpeg-turbo/issues/17

Without this change, poppler fails to build on newer LLVMs, as a transitive dependency was removed.