Add #include <unistd.h> to filesys.cpp (needed by some linux distros now)

src/filesys.cpp

@@ -171,6 +171,7 @@ bool RecursiveDelete(std::string path)
 #include <errno.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
+#include <unistd.h>
 
 std::vector<DirListNode> GetDirListing(std::string pathstring)
 {