MFH: r440334 r441969

Fix library updating

Details:
Apparently, clang optimises exceptions with attribute((pure))
more aggressively than gcc, causing mpd to not notice files removed
from the library. This patch causes mpd to be built without the pure
attribute.

PR: 219048
Reported by: hideo@lastamericanempire.com

Update to upstream version 0.20.8

Approved by: ports-secteam (feld)