[v4] Fix for CMake error when calling set_property on aliased targets

[rh101]

ALIAS targets are non-modifiable, so set_property cannot be called on them. This fix will attempt to extract the real target from the alias, and if it exists, it will use that target value for the call to set_property.

This issue appeared when using CMake 3.20.2 when attempting to compile for iOS.

In addition to that, the lists generated by both search_depend_libs_recursive and get_target_depends_ext_dlls will have any duplicate entries removed, since the entries were being processed multiple times in later sections of code.