Caveat when using setvbuf/fread on Android

The standard library function setvbuf() can be used to set unbuffered mode for a stream. However, fread() on Android has the behavior that, in unbuffered mode, it can sometimes return EOF, or (size_t)(−1), instead of the number of elements actually read. This unexpected behavior was the cause for bug 935831.

I took a glance at the few other places where Gecko uses unbuffered mode, and fortunately, it appears none of them apply to a regular Android run.