cmake: Fix code style for consistency Indentation to 4 spaces Prefer lower case for functions and macros

cmake: Move join() to helper functions module

cmake: Fix osx-related issues with cmake-build Add new helper function to retrive pkg-config variables in Cmake; use paths defined as environment variables for builds on OS X (useful if MacPorts is not installed into default prefix); check backend of GTK2 on OS X in main cmake file (x11|quartz).