CMake: Avoid using pkg-config to find libiio
CMake: Avoid using pkg-config to find libiio

It is not very convenient for Windows builds.

Signed-off-by: Paul Cercueil <73d292422978d45c9eeef455bb1b24a0db453722@analog.com>

analogdevicesinc/libad9361-iio,analogdevicesinc/libad9361-iio,analogdevicesinc/libad9361-iio,analogdevicesinc/libad9361-iio