icu: Expand is_linux to is_linux || is_chromeos. Currently is_linux is set to true on Chrome OS build, but it is planned to be set to false. This is the preparation. Bug: chromium:1110266 Test: Built locally. Change-Id: I63232a5ccad4c0cbc6e789693dbb2ccecc475ae3 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/deps/icu/+/2400838 Reviewed-by: Jungshik Shin <jshin@chromium.org>