I noticed that the -use-linker-plugin option seems to be passed to the linker. This is because LINK_COMMAND_SPEC includes %{u*}. And that is because -uSYMBOL is a documented linker option.
The effect is that the linker creates an undefined reference to the symbol "se-linker-plugin". Any user unfortunate enough to link against a library which contains a definition of that symbol may see an unexpected result. Admittedly unlikely, but still. I think we need to fix this option before the release to not overlap with any existing linker options. Ian