Fix bugs and make code tinier

- Fixed bug where stdio eof wasn't being sticky
- Fixed bug where fseeko() wasn't clearing eof state
- Removed assert() usage from libc favoring _unassert() / _npassert()

libc/stdio/clearerr.c

@@ -20,7 +20,7 @@
 #include "libc/stdio/stdio.h"
 
 /**
- * Clears error state on stream.
+ * Clears eof and error state indicators on stream.
  *
  * @param f is file object stream pointer
  * @see	clearerr_unlocked()