Don't disable configure cache if system libs not allowed
Don't disable configure cache if system libs not allowed

On certain platform, allow_system_libs is False, in which case there is
no need to disable configure cache.

davibe/cerbero,ford-prefect/cerbero,multipath-rtp/cerbero,BigBrother-International/gst-cerbero,fluendo/cerbero,centricular/cerbero,lubosz/cerbero,nirbheek/cerbero-old,brion/cerbero,ramaxlo/cerbero,jackjansen/cerbero-2013,AlertMe/cerbero,justinjoy/cerbero,jackjansen/cerbero,ikonst/cerbero,brion/cerbero,ikonst/cerbero,GStreamer/cerbero,ford-prefect/cerbero,BigBrother-International/gst-cerbero,BigBrother-International/gst-cerbero,nirbheek/cerbero-old,sdroege/cerbero,cee1/cerbero-mac,superdump/cerbero,fluendo/cerbero,lubosz/cerbero,freedesktop-unofficial-mirror/gstreamer__cerbero,sdroege/cerbero,centricular/cerbero,flexVDI/cerbero,ramaxlo/cerbero,ford-prefect/cerbero,flexVDI/cerbero,ramaxlo/cerbero,OptoFidelity/cerbero,nicolewu/cerbero,shoreflyer/cerbero,EricssonResearch/cerbero,freedesktop-unofficial-mirror/gstreamer-sdk__cerbero,shoreflyer/cerbero,flexVDI/cerbero,ikonst/cerbero,brion/cerbero,nicolewu/cerbero,sdroege/cerbero,sdroege/cerbero,ramaxlo/cerbero,nzjrs/cerbero,OptoFidelity/cerbero,freedesktop-unofficial-mirror/gstreamer-sdk__cerbero,nirbheek/cerbero-old,jackjansen/cerbero,ylatuya/cerbero,justinjoy/cerbero,freedesktop-unofficial-mirror/gstreamer__sdk__cerbero,freedesktop-unofficial-mirror/gstreamer-sdk__cerbero,OptoFidelity/cerbero,nicolewu/cerbero,BigBrother-International/gst-cerbero,centricular/cerbero,fluendo/cerbero,nirbheek/cerbero,multipath-rtp/cerbero,ikonst/cerbero,cee1/cerbero-mac,ylatuya/cerbero,multipath-rtp/cerbero,nzjrs/cerbero,AlertMe/cerbero,GStreamer/cerbero,nzjrs/cerbero,centricular/cerbero,nirbheek/cerbero-old,lubosz/cerbero,nzjrs/cerbero,shoreflyer/cerbero,centricular/cerbero,atsushieno/cerbero,freedesktop-unofficial-mirror/gstreamer__sdk__cerbero,freedesktop-unofficial-mirror/gstreamer__sdk__cerbero,flexVDI/cerbero,freedesktop-unofficial-mirror/gstreamer__cerbero,jackjansen/cerbero-2013,ikonst/cerbero,nirbheek/cerbero,EricssonResearch/cerbero,GStreamer/cerbero,cee1/cerbero-mac,AlertMe/cerbero,jackjansen/cerbero,atsushieno/cerbero,shoreflyer/cerbero,EricssonResearch/cerbero,justinjoy/cerbero,GStreamer/cerbero,nirbheek/cerbero,GStreamer/cerbero,davibe/cerbero,jackjansen/cerbero-2013,superdump/cerbero,BigBrother-International/gst-cerbero,jackjansen/cerbero-2013,fluendo/cerbero,freedesktop-unofficial-mirror/gstreamer-sdk__cerbero,jackjansen/cerbero-2013,jackjansen/cerbero,shoreflyer/cerbero,sdroege/cerbero,lubosz/cerbero,nirbheek/cerbero,fluendo/cerbero,EricssonResearch/cerbero,davibe/cerbero,brion/cerbero,freedesktop-unofficial-mirror/gstreamer__cerbero,freedesktop-unofficial-mirror/gstreamer__cerbero,ramaxlo/cerbero,superdump/cerbero,atsushieno/cerbero,EricssonResearch/cerbero,AlertMe/cerbero,OptoFidelity/cerbero,flexVDI/cerbero,freedesktop-unofficial-mirror/gstreamer-sdk__cerbero,superdump/cerbero,ylatuya/cerbero,nzjrs/cerbero,ylatuya/cerbero,atsushieno/cerbero,cee1/cerbero-mac,AlertMe/cerbero,ford-prefect/cerbero,davibe/cerbero,freedesktop-unofficial-mirror/gstreamer__sdk__cerbero,multipath-rtp/cerbero,multipath-rtp/cerbero,justinjoy/cerbero,atsushieno/cerbero,brion/cerbero