Don't pretend unresolved symbols are an error

Merged Peter Hutterer requested to merge whot/xkbcomp:wip/unresolved-symbol-warning into master

Whenever xkeyboard-config is newer than xorgproto, or libX11 just hasn't yet been rebuilt against the protocol we end up with some unresolved symbols. That's not an error, it just happens. Let's downgrade this to a warning instead

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