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

Backport: release