Fix round() macro conflict between math.h and wiring.h

The AVR LIBC v1.7.1 and greater has their own definition
of round().

Change-Id: I6b1578a7df4c47c6301fc24d91067c2198f035ff
Signed-off-by: Adam Hampson <ahampson@google.com>
Merge tag 'android-4.3_r2.1' into jellybean-mr2.1

Android 4.3 release 2.1