Set CMake variable X11_SUPPORTED for all systems that have X11.
Adjust _adjust_library_map() in util/cmake/helper.py to apply X11_SUPPORTED
condition around X11 related packages instead of just LINUX.
Adjust configure.cmake in src/gui based on this change.
Why, because X11 is not just Linux.
Change-Id: Ic3c04eaa55301d1237c7e74281eccd4f8e27e9ce
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>