GN: Revert to default compiler optimizations for Win Release.
GN: Revert to default compiler optimizations for Win Release.

Revert back to the GN/Chromium default optimization levels what
was changed in https://codereview.webrtc.org/2307283002/ and
https://codereview.webrtc.org/2305403002/ due to a performance
regression. Those changes caused a size regression in Chromium,
which is why this is changed back.

BUG=chromium:641966
NOTRY=True
TBR=ehmaldonado@webrtc.org, henrik.lundin@webrtc.org

Review-Url: https://codereview.webrtc.org/2334593002
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#14178}

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