graphics/poppler: update to 21.09

Release 21.09.0:
        core:
         * Splash: Massive speed improvement on files that use lots of save/restore (q/Q) operators
         * Correct decoding of signature properties Reason & Location when they are Unicode
         * Fix issues with malformed files
         * MSVC build fixes

        build system:
         * Call cmake_minium_required() before project()
         * Always append to CMAKE_{C,CXX}_FLAGS_${CMAKE_BUILD_TYPE}
         * correctly forward user-provided flags to try_compile()

Exp-run by:	antoine
PR:		258206