update to latest upstream master
Squashed 'libmediaart/' changes from 762f87c..5167238

5167238 build: Don't forget to define LIBMEDIAART_BACKEND for all Qt cases

git-subtree-dir: libmediaart
git-subtree-split: 5167238b677be4f5a37dd08c190b495fad94bf2a
Merge commit '6cf6019a440a047006b6d05a1912628f9b3ee01a'