Remove Apple-only GCC_WARN_ABOUT_MISSING_NEWLINE

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/199843003

Patch from Ben Noordhuis <ben@strongloop.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20435 ce2b1a6d-e550-0410-aec6-3dcde31c8c00