build-tools: fix deadlock in autoconf's configure check for M4
build-tools: fix deadlock in autoconf's configure check for M4

nzjrs/cerbero,superdump/cerbero,nirbheek/cerbero,brion/cerbero,nirbheek/cerbero-old,nirbheek/cerbero,nzjrs/cerbero,ikonst/cerbero,justinjoy/cerbero,brion/cerbero,multipath-rtp/cerbero,freedesktop-unofficial-mirror/gstreamer__sdk__cerbero,freedesktop-unofficial-mirror/gstreamer__sdk__cerbero,nirbheek/cerbero-old,jackjansen/cerbero,AlertMe/cerbero,ramaxlo/cerbero,flexVDI/cerbero,OptoFidelity/cerbero,lubosz/cerbero,GStreamer/cerbero,jackjansen/cerbero,lubosz/cerbero,multipath-rtp/cerbero,ford-prefect/cerbero,atsushieno/cerbero,ylatuya/cerbero,freedesktop-unofficial-mirror/gstreamer__cerbero,flexVDI/cerbero,EricssonResearch/cerbero,flexVDI/cerbero,centricular/cerbero,nirbheek/cerbero,fluendo/cerbero,davibe/cerbero,ikonst/cerbero,ikonst/cerbero,fluendo/cerbero,atsushieno/cerbero,EricssonResearch/cerbero,AlertMe/cerbero,fluendo/cerbero,EricssonResearch/cerbero,justinjoy/cerbero,superdump/cerbero,OptoFidelity/cerbero,sdroege/cerbero,AlertMe/cerbero,brion/cerbero,atsushieno/cerbero,sdroege/cerbero,sdroege/cerbero,ramaxlo/cerbero,AlertMe/cerbero,ylatuya/cerbero,lubosz/cerbero,ikonst/cerbero,freedesktop-unofficial-mirror/gstreamer__sdk__cerbero,nirbheek/cerbero-old,GStreamer/cerbero,ramaxlo/cerbero,shoreflyer/cerbero,sdroege/cerbero,nirbheek/cerbero-old,shoreflyer/cerbero,davibe/cerbero,multipath-rtp/cerbero,AlertMe/cerbero,EricssonResearch/cerbero,brion/cerbero,jackjansen/cerbero,nzjrs/cerbero,multipath-rtp/cerbero,nirbheek/cerbero,ford-prefect/cerbero,nzjrs/cerbero,jackjansen/cerbero,davibe/cerbero,EricssonResearch/cerbero,shoreflyer/cerbero,lubosz/cerbero,OptoFidelity/cerbero,freedesktop-unofficial-mirror/gstreamer__cerbero,brion/cerbero,GStreamer/cerbero,freedesktop-unofficial-mirror/gstreamer__cerbero,ramaxlo/cerbero,flexVDI/cerbero,GStreamer/cerbero,freedesktop-unofficial-mirror/gstreamer__sdk__cerbero,fluendo/cerbero,superdump/cerbero,GStreamer/cerbero,ramaxlo/cerbero,atsushieno/cerbero,justinjoy/cerbero,ford-prefect/cerbero,centricular/cerbero,nzjrs/cerbero,shoreflyer/cerbero,fluendo/cerbero,flexVDI/cerbero,ikonst/cerbero,ylatuya/cerbero,ford-prefect/cerbero,ylatuya/cerbero,davibe/cerbero,multipath-rtp/cerbero,centricular/cerbero,shoreflyer/cerbero,atsushieno/cerbero,centricular/cerbero,OptoFidelity/cerbero,centricular/cerbero,superdump/cerbero,justinjoy/cerbero,freedesktop-unofficial-mirror/gstreamer__cerbero,sdroege/cerbero