GN: Fix common_audio linking on iOS
GN: Fix common_audio linking on iOS

The invalid condition made the test be included for iOS, which
fails linking.

BUG=webrtc:5949, webrtc:5544
NOTRY=True

Review-Url: https://codereview.webrtc.org/2291023002
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#13970}

TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc