list: Fix docs for APPEND to show that elements are optional

list(APPEND) has been able to append nothing since commit a06dcdba
(Allow LIST(APPEND) command to append nothing, 2008-01-16) but the
documentation still used to imply that at least one argument is
required.
Merge topic 'doc-list-append-nothing' into next

eec7834 list: Fix docs for APPEND to show that elements are optional
Fix excluded configurations from running the InterfaceBuildTargets test.
Merge topic 'INTERFACE_LIBRARY-build-targets' into next

df46250 Fix excluded configurations from running the InterfaceBuildTargets test.
Create make rules for INTERFACE_LIBRARY targets.

The result is that the depends of the target are created.

So,

 add_library(somelib foo.cpp)
 add_library(anotherlib EXCLUDE_FROM_ALL foo.cpp)
 add_library(extra EXCLUDE_FROM_ALL foo.cpp)
 target_link_libraries(anotherlib extra)

 add_library(iface INTERFACE)
 target_link_libraries(iface INTERFACE anotherlib)

Executing 'make iface' will result in the anotherlib and extra targets
being made.

Adding a regular executable to the INTERFACE of an INTERFACE_LIBRARY
will not result in the executable being built with 'make iface' because
of the logic in cmComputeTargetDepends::AddTargetDepend.

So far, this is implemented only for the Makefile generator. Other
generators will follow if this feature is possible for them.
Merge topic 'INTERFACE_LIBRARY-build-targets' into next

a6c9d93 Create make rules for INTERFACE_LIBRARY targets.