Fix the Mac build. "_toolset" needs to be tested inside target_conditions now.

And there is no need to have -llog any more.

Review URL: http://codereview.chromium.org/8631012
Patch from Jing Zhao <jingzhao@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10057 ce2b1a6d-e550-0410-aec6-3dcde31c8c00