Only use -lm on Linux in ISAC.

Remove unneeded WEBRTC_LINUX define.

BUG=crbug.com/298656
TESTED=Passed trybots.
R=wjia@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/2313004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@4865 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed