Add basic symlink support.

- sys$readlink + readlink()
- Add a /proc/PID/exe symlink to the process's executable.
- Print symlink contents in ls output.
- Some work on plumbing options into VFS::open().

LibC/unistd.h

@@ -7,7 +7,7 @@ extern "C" {
 uid_t getuid();
 gid_t getgid();
 pid_t getpid();
-int open(const char* path);
+int open(const char* path, int options);
 ssize_t read(int fd, void* buf, size_t count);
 int close(int fd);
 pid_t waitpid(pid_t, int* wstatus, int options);
@@ -16,6 +16,7 @@ char* getcwd(char* buffer, size_t size);
 int lstat(const char* path, stat* statbuf);
 int sleep(unsigned seconds);
 int gethostname(char*, size_t);
+ssize_t readlink(const char* path, char* buffer, size_t);
 
 #define WEXITSTATUS(status) (((status) & 0xff00) >> 8)
 #define WTERMSIG(status) ((status) & 0x7f)
@@ -52,4 +53,10 @@ int gethostname(char*, size_t);
 #define S_ISFIFO(m) (((m) & S_IFMT) == S_IFIFO)
 #define S_ISLNK(m) (((m) & S_IFMT) == S_IFLNK)
 
+#define O_RDONLY 0
+#define O_WRONLY 1
+#define O_RDWR 2
+#define O_DIRECTORY 00200000
+#define O_NOFOLLOW 00400000
+
 }