Set -Wno-unused-result only when chromeos==0.
Set -Wno-unused-result only when chromeos==0.

-Wno-unused-result is not supported by gcc 4.3.4, which is used for building
chrome in chroot, and setting this option causes build error when building
chrome from the source in chroot for Chrome OS.

http://build.chromium.org/p/chromiumos/builders/x86%20generic%20tot%20chrome%20pre%20flight%20queue

(Need to copy URL text instead of clicking the link to see the page above.)

BUG=chromium-os:18272
TEST=emerge-x86-alex chromeos-chrome succeeds.


Review URL: http://codereview.chromium.org/7517007

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@94266 0039d316-1c4b-4281-b951-d872f2087c98

gavinp/chromium,yitian134/chromium,yitian134/chromium,yitian134/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,gavinp/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,gavinp/chromium,adobe/chromium,adobe/chromium,ropik/chromium,ropik/chromium,yitian134/chromium,yitian134/chromium,gavinp/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,gavinp/chromium,adobe/chromium,gavinp/chromium,gavinp/chromium,gavinp/chromium,gavinp/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,adobe/chromium,ropik/chromium,ropik/chromium,gavinp/chromium