If you use a wizard-created project, please check the compiler and linker settings:
"Build options -> [your project] -> Compiler settings -> Other compiler settings" and
"Build options -> [your project] -> Linker settings -> Other linker options".
Both will refer to gtk+2.0 pkg-config files, but Debian based distros (most others nowadays also) use gtk3 as default.
So you have to fix these entries to point to the correct gtk-devel files.
It should be enough to change the "2" to a "3".
You can check it on a console.
You might need to close and reopen C::B to make this be recognized.