genex-LINK_LIBRARY: ensure correct generation inside LINK_GROUP genex

This fix ensures the following pattern is correctly handled:
$<LINK_GROUP:group_feat,$<LINK_LIBRARY:lib_feat,mylib>>

With:
CMAKE_LINK_GROUP_USING_group_feat = "—START_GROUP" "—END_GROUP"
CMAKE_LINK_LIBRARY_USING_lib_feat = "—PREFIX" "—LINK <LIBRARY>" "—SUFFIX"

Before the fix, we get the following generation:
—START_GROUP —PREFIX —LINK /path/to/mylib —END_GROUP —SUFFIX
—END_GROUP and —SUFFIX are in the wrong order

After the fix, we get the correct order:
—START_GROUP —PREFIX —LINK /path/to/mylib —SUFFIX —END_GROUP