cmake-gui: Attach icons only to main GUI executables

Brad Kingrequested to merge
brad.king/cmake:cmake-gui-res into master

In !5361 (merged) and !5362 (merged) we attached the icon source files to all consumers of CMakeGUILib, but that includes other libraries like CMakeGUIMainLib. The latter library is meant only for direct consumption by a GUI executable, so use that to propagate the icons instead.

Backport: release

Edited by Brad King

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