[CMake] Variable TTL_LIBS debug/optimized keywords are getting eaten

[Neumann-A]

https://github.com/Unidata/netcdf-c/blob/29d070c50f1d02edbe5796ca9483345441570aab/liblib/CMakeLists.txt#L103

This line removes duplicates of debug/optimized keywords in TTL_LIBS which is probably not intended and screws up the generated targets with missing generator expressions