Remove unused forward declarations.
Generate config-specific interface link libraries propeties.

All other properties we generate are config-specific, so it makes
sense to do so here too.
Merge topic 'minor-fixes' into next

ba48e63 Generate config-specific interface link libraries propeties.
deb51a7 Remove unused forward declarations.
CPackRPM fix #13898 uses IF(DEFINED var) to avoid wrong var value logic
Merge topic 'CPackRPM-fixSomeRPMSpecificVarHandling' into next

9be3da1 CPackRPM fix #13898 uses IF(DEFINED var) to avoid wrong var value logic