fix 'make clean': shell glob, ignore failure

Unfortunately a glob like osmo-x__*.{svg,png} doesn't work, so have the
suffixes in separate globs.

Add dashes to indicate that failure should be ignored.

Change-Id: I6bc4d9ea72b43a573acbc860c23397f748de2c7b
1 file changed
tree: 85acb086ab9920ac6d4b2a85cedc3b52bbe6b6e1
  1. doc/