Log Message:
poppler: update to 21.07.0.

Release 21.07.0:
        core:
         * JBIG2Stream: Do not consider a size-0 to be an error. Issue #535
         * PSOutputDev: fix off-by-one error for image masking in L1/L2 output. \ 
Issue #1088
         * CairoOutputDev: Fix memory leak on broken files
         * Minor code improvements

        build system:
         * set C standard to 11 without extensions