Get GNU GMP test suite fully passing

- Fix stdio fmemopen() buffer behaviors
- Fix scanf() to return EOF when appropriate
- Prefer fseek/ftell names over fseeko/ftello
- Ensure locale field is always set in the TIB
- Fix recent regression in vfprintf() return count
- Make %n directive in scanf() have standard behavior

libc/stdio/rewind.c

@@ -29,7 +29,7 @@
  */
 void rewind(FILE *f) {
   flockfile(f);
-  fseeko_unlocked(f, 0, SEEK_SET);
+  fseek_unlocked(f, 0, SEEK_SET);
   f->state = 0;
   funlockfile(f);
 }