Fix plugin cmake for release only

[gassmoeller]

This PR is a fix for #6017. The problem was that if we build ASPECT in release only mode and then set up an external library, the user already sets up a target with the original library name (${_target}) in the CMakeLists.txt of the plugin. Then the macro in AspectConfig.cmake.in would set up another target with name ${_target}.release, and only for this additional target would it configure the correct include files. But when running make the makefile would then try to compile both targets (with the same sources, but only one of them had correctly configured header files).

I changed the macro to now reuse the target name from the user CMakeLists for the release library. If no debug library is compiled, no new target name is necessary (this means the release target has a different name depending on whether a debug target exists).

I also modified the creation of the symbolic links at the end, so that all existing ASPECT executables (aspect-debug and/or aspect-release) and the generic link aspect are available in the plugin directory.

[tjhei]

Awesome, thank you.

[bangerth]

Thanks, and my apologies for not getting around to this in time :-(

[gassmoeller]

No worries, luckily once I had read myself into the CMake file it was simpler than expected.