Because on gcc, cast to void doesn't silence the warning. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66425 Also add an RTC_ prefix to the macro instead of only defining it if it wasn't already defined, to ensure that we always get our own version. BUG=none Review-Url: https://codereview.webrtc.org/2797983003 Cr-Commit-Position: refs/heads/master@{#17563}