aom_ports: Fix build in Xcode 8.

Use void casts and avoid unused/unnamed parameter warnings.

Change-Id: Id02ec2c613cb1423f693bcc56832ccd9b41d05bd

aom_ports/aom_timer.h

diff --git a/aom_ports/aom_timer.h b/aom_ports/aom_timer.h
index d684c3a..904f2fe 100644
--- a/aom_ports/aom_timer.h
+++ b/aom_ports/aom_timer.h
@@ -97,11 +97,12 @@
   void *dummy;
 };
 
-static INLINE void aom_usec_timer_start(struct aom_usec_timer * /*t*/) {}
+static INLINE void aom_usec_timer_start(struct aom_usec_timer *t) { (void)t; }
 
-static INLINE void aom_usec_timer_mark(struct aom_usec_timer * /*t*/) {}
+static INLINE void aom_usec_timer_mark(struct aom_usec_timer *t) { (void)t; }
 
-static INLINE int aom_usec_timer_elapsed(struct aom_usec_timer * /*t*/) {
+static INLINE int aom_usec_timer_elapsed(struct aom_usec_timer *t) {
+  (void)t;
   return 0;
 }