Include signal.h jointly for POSIX systems
Include signal.h jointly for POSIX systems

Otherwise, for example, FreeBSD the build fails due to SIGKILL not being
around.

Haxi52/cuberite,marvinkopf/cuberite,nounoursheureux/MCServer,electromatter/cuberite,QUSpilPrgm/cuberite,Howaner/MCServer,nounoursheureux/MCServer,kevinr/cuberite,nounoursheureux/MCServer,ionux/MCServer,SamOatesPlugins/cuberite,Howaner/MCServer,nichwall/cuberite,birkett/MCServer,marvinkopf/cuberite,mjssw/cuberite,kevinr/cuberite,marvinkopf/cuberite,birkett/cuberite,mjssw/cuberite,Frownigami1/cuberite,SamOatesPlugins/cuberite,birkett/cuberite,Schwertspize/cuberite,mc-server/MCServer,birkett/MCServer,Haxi52/cuberite,marvinkopf/cuberite,kevinr/cuberite,birkett/MCServer,QUSpilPrgm/cuberite,johnsoch/cuberite,mjssw/cuberite,kevinr/cuberite,birkett/MCServer,QUSpilPrgm/cuberite,Haxi52/cuberite,birkett/cuberite,birkett/cuberite,nichwall/cuberite,birkett/cuberite,Fighter19/cuberite,ionux/MCServer,HelenaKitty/EbooMC,Fighter19/cuberite,mjssw/cuberite,HelenaKitty/EbooMC,electromatter/cuberite,bendl/cuberite,Haxi52/cuberite,johnsoch/cuberite,nounoursheureux/MCServer,SamOatesPlugins/cuberite,nounoursheureux/MCServer,Altenius/cuberite,Fighter19/cuberite,Schwertspize/cuberite,tonibm19/cuberite,HelenaKitty/EbooMC,bendl/cuberite,electromatter/cuberite,Howaner/MCServer,Frownigami1/cuberite,mjssw/cuberite,ionux/MCServer,bendl/cuberite,mc-server/MCServer,HelenaKitty/EbooMC,Haxi52/cuberite,bendl/cuberite,ionux/MCServer,johnsoch/cuberite,ionux/MCServer,tonibm19/cuberite,Howaner/MCServer,mjssw/cuberite,mc-server/MCServer,bendl/cuberite,birkett/MCServer,johnsoch/cuberite,kevinr/cuberite,Howaner/MCServer,mc-server/MCServer,Frownigami1/cuberite,electromatter/cuberite,Fighter19/cuberite,Altenius/cuberite,marvinkopf/cuberite,nounoursheureux/MCServer,Schwertspize/cuberite,Haxi52/cuberite,QUSpilPrgm/cuberite,mc-server/MCServer,kevinr/cuberite,tonibm19/cuberite,nichwall/cuberite,Altenius/cuberite,Howaner/MCServer,tonibm19/cuberite,nichwall/cuberite,nichwall/cuberite,Frownigami1/cuberite,Altenius/cuberite,ionux/MCServer,tonibm19/cuberite,SamOatesPlugins/cuberite,HelenaKitty/EbooMC,marvinkopf/cuberite,Frownigami1/cuberite,Schwertspize/cuberite,QUSpilPrgm/cuberite,Altenius/cuberite,birkett/cuberite,SamOatesPlugins/cuberite,Schwertspize/cuberite,mc-server/MCServer,Fighter19/cuberite,birkett/MCServer,johnsoch/cuberite,electromatter/cuberite,electromatter/cuberite,QUSpilPrgm/cuberite,tonibm19/cuberite,Fighter19/cuberite,nichwall/cuberite