Add a comment to MacPrefixHeader. Also try to unbreak make generator on linux.
Add a comment to MacPrefixHeader. Also try to unbreak make generator on linux.

TBR=evan
Review URL: http://codereview.chromium.org/7388016
old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google