UseCorrade.cmake: fixing .metadata's output directory

[xiconxi]

UseCorrade.cmake: fixing custom-target<*.metadata> whileCMAKE_LIBRARY_OUTPUT_DIRECTORY is setted

[mosra]

Hi, thank you for the contribution!

I wonder, would this work also if $<TARGET_FILE_DIR:${plugin_name}> was used instead of ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_CFG_INTDIR}? That would fix it to not require the extra branch.

The other function, corrade_create_plugins_symlink_for_executable(), is not used from any place and I think it could live in your codebase for now instead? As I mentioned in another issue, making this work better is on my list, so when that's done, this function shouldn't be needed anymore.

[xiconxi]

I haven't use cmake-generator-expressions before, that's much better than mine。

[mosra]

Commited in bb45552, hopefully it works for you the way it should :)