Fix linking ffmpeg frameworks on 10.7. Fixes #34963

FFmpeg changed the link frameworks in http://git.videolan.org/?p=ffmpeg.git;a=commitdiff;h=a6555f88aaf0730e64240136fb19d8effb3a0738
(ApplicationServices -> CoreGraphics)
This reverts that change for Lion and below

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Apologies - I'm not sure on the convention of making patches to existing code. Is an inline edit using Perl acceptable?!

Fixes #34963