Merge topic 'FindGTK2-targets'

7efef02d FindGTK2: Add tests for components and targets in gtk and gtkmm modules
95fc47aa FindGTK2: Make pangocairo and cairo optional dependencies
26f790f0 FindGTK2: Change extra includes -> optional
24e0272b FindGTK2: do not skip target creation if optional dependencies are not found
d5f130cd FindGTK2: Refactor _GTK2_ADJUST_LIB_VARS into _GTK2_ADD_TARGET
fffbd725 FindGTK2: Do not add freetype includes if they are not found
b69720d9 FindGTK2: Add libraries to the GTK2_LIBRARIES variable only when found
425ec408 FindGTK2: Do not link libfreetype
e9f46dfe FindGTK2: Add config directories only if different from include ones
56a79e1f FindGTK2: Set INTERFACE_COMPILE_DEFINITIONS target property only if not empty
4b47586a FindGTK2: Add check to ensure that target exists
61242ccc FindGTK2: Fix gmodule, glibmm, pangoft2, and pangoxft targets
4b876de9 FindGTK2: Link freetype libs to targets including freetype includes
67e761fa FindGTK2: Small cleanup
682eea39 FindGTK2: Do not require the GTK_ prefix in all the internal functions
0bc3763c FindGTK2: Better handling of include directories
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