A previous CL (https://codereview.webrtc.org/2281513002) broke Windows, Mac and Linux bots in WebRTC's Chromium FYI, by suppressing these warnings when they hadn't been set. This CL fixes it suppressing warnings only on Windows. Example failures: https://build.chromium.org/p/chromium.webrtc.fyi/builders/Win%20Builder/builds/6540 https://build.chromium.org/p/chromium.webrtc.fyi/builders/Mac%20Builder/builds/16588 https://build.chromium.org/p/chromium.webrtc.fyi/builders/Linux%20Builder/builds/9655 BUG=webrtc:6255 NOTRY=True Review-Url: https://codereview.webrtc.org/2284333002 Cr-Commit-Position: refs/heads/master@{#13951}