build-tools: update automake to 1.15.1
build-tools: update automake to 1.15.1

Fixes build with perl 5.26

help2man: can't get `--help' info from automake-1.15
Try `--no-discard-stderr' if option outputs to stderr
make: *** [Makefile:3687: doc/automake-1.15.1] Error 255

nirbheek/cerbero,EricssonResearch/cerbero,flexVDI/cerbero,EricssonResearch/cerbero,atsushieno/cerbero,fluendo/cerbero,atsushieno/cerbero,GStreamer/cerbero,flexVDI/cerbero,fluendo/cerbero,nirbheek/cerbero,fluendo/cerbero,centricular/cerbero,flexVDI/cerbero,EricssonResearch/cerbero,atsushieno/cerbero,GStreamer/cerbero,GStreamer/cerbero,fluendo/cerbero,EricssonResearch/cerbero,EricssonResearch/cerbero,centricular/cerbero,nirbheek/cerbero,flexVDI/cerbero,centricular/cerbero,centricular/cerbero,atsushieno/cerbero,GStreamer/cerbero,fluendo/cerbero,atsushieno/cerbero,centricular/cerbero,nirbheek/cerbero,GStreamer/cerbero,flexVDI/cerbero