[100%] Building CXX object src/CMakeFiles/widelands.dir/main.cc.o
/opt/widelands/src/main.cc: In function ‘int main(int, char**)’:
/opt/widelands/src/main.cc:72:19: error: ‘fork’ was not declared in this scope
/opt/widelands/src/main.cc:77:11: error: ‘setsid’ was not declared in this scope
/opt/widelands/src/main.cc:79:10: error: ‘STDIN_FILENO’ was not declared in this scope
/opt/widelands/src/main.cc:79:22: error: ‘close’ was not declared in this scope
/opt/widelands/src/main.cc:80:10: error: ‘STDOUT_FILENO’ was not declared in this scope
/opt/widelands/src/main.cc:81:10: error: ‘STDERR_FILENO’ was not declared in this scope
/opt/widelands/src/main.cc:84:20: error: ‘dup’ was not declared in this scope
make[2]: *** [src/CMakeFiles/widelands.dir/main.cc.o] Error 1
make[1]: *** [src/CMakeFiles/widelands.dir/all] Error 2
make: *** [all] Error 2