plugins: Fix stupid #if mistake in UIUGens.cpp

Signed-off-by: Scott Wilson <i@scottwilson.ca>
qt: Rename hacks_mac.M to hacks_mac.mm to deal with Xcode being fussy

Recent Xcode no longer infers obj-c++ compilation for .M files and wants .mm or a manual setting. This change means that it is possible to generate an Xcode project from cmake and compile it without errors, at least on Xcode 4.6 anf OSX 10.8.

Signed-off-by: Scott Wilson <i@scottwilson.ca>