PREFERRED PROVIDER for jpeg and jpeg-native

This combined with building some packages can lead to a dreadful error message.

NOTE: multiple providers are available for jpeg (jpeg, libjpeg-turbo)
NOTE: consider defining a PREFERRED_PROVIDER entry to match jpeg
NOTE: multiple providers are available for jpeg-native (jpeg-native, libjpeg-turbo-native)
NOTE: consider defining a PREFERRED_PROVIDER entry to match jpeg-native

To solve the problem, insert this is local.conf (or a distro conf file):

PREFERRED_PROVIDER_jpeg = "jpeg"
PREFERRED_PROVIDER_jpeg-native = "jpeg-native"