Stub out poll() syscall and LibC wrapper.

Kernel/Process.h

@@ -157,6 +157,7 @@ public:
     int sys$munmap(void*, size_t size);
     int sys$set_mmap_name(void*, size_t, const char*);
     int sys$select(const Syscall::SC_select_params*);
+    int sys$poll(pollfd*, int nfds, int timeout);
     ssize_t sys$get_dir_entries(int fd, void*, size_t);
     int sys$getcwd(char*, size_t);
     int sys$chdir(const char*);