Increase header padding for ld

This allows me to build emacs once again with the following options. I hadn't tried to build from HEAD in awhile, but found it not working today.

    brew install --HEAD --cocoa --srgb --use-git-head emacs

I haven't done tests to see if the padding needs to be changed for other options, I'm not sure if the wasted space is worth finding the optimal value for each.