Break OSX (aka: add an OBJC file for OSX compiles)

(cherry picked from commit 93481c60e75f56b743a00a0022540bc1f504aef7)
Revert "OSX HiDPI: update package building instructions"

This reverts commit ff955eae31a5a53876f65841c41b1ce1bb2174b5.

(cherry picked from commit 8a2cfb9a84e3bc025dee600bd82038110db4bbb2)
OSX HiDPI: move PPD detection from GTK patch to in-tree file

(cherry picked from commit 5d36053f39d804ec393dc9bbf1774669a197e7ce)