simulator: makefile: compile fix under Ubuntu
simulator: makefile: compile fix under Ubuntu

Apparently, --as-needed is passed to the linker by default on Ubuntu. In this case, the linker fails to notice that the pthread library will be needed by std::thread and thus would never link it. This would result in std::thread throwing exceptions on start.

walachey/football-worldcup-simulator,walachey/football-worldcup-simulator,walachey/football-worldcup-simulator-comp,walachey/football-worldcup-simulator-comp,walachey/football-worldcup-simulator,walachey/football-worldcup-simulator,walachey/football-worldcup-simulator-comp,walachey/football-worldcup-simulator-comp,walachey/football-worldcup-simulator