Trivial, obvious counterpart to the standard ferror(3) and clearerr(3),
and lets us build bison out of the box.
Bug: http://b/64273806
Test: ran tests
Change-Id: I20affabddb71210051165c41e86adfe5ae04f77f
Implement __freading and __fwriting, and clarify the documentation that was
the cause of these not being implemented for years.
Bug: http://b/17157253
Test: ran tests
Change-Id: I89542c8131b13889e2585417a024050ecf2abcb7