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_unlocked.c

@@ -18,6 +18,13 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/stdio/stdio.h"
 
+/**
+ * Clears eof and error state indicators on stream.
+ *
+ * @param f is file object stream pointer
+ * @see	clearerr()
+ * @threadsafe
+ */
 void clearerr_unlocked(FILE *f) {
   f->state = 0;
 }