Revert "Use libc++ as stdlib for Clang."
Revert "Use libc++ as stdlib for Clang."

This reverts commit a514619022900bc8b917518a9cf93aae075de611.

Default stdlib should be better on most distributions. Since both Ubuntu
and Debian currently have still issues depending on clang's and gcc's version
we hope the default is most reliable.

RabadanLab/MITKats,MITK/MITK,RabadanLab/MITKats,fmilano/mitk,fmilano/mitk,fmilano/mitk,iwegner/MITK,MITK/MITK,iwegner/MITK,MITK/MITK,MITK/MITK,RabadanLab/MITKats,iwegner/MITK,iwegner/MITK,fmilano/mitk,fmilano/mitk,iwegner/MITK,iwegner/MITK,MITK/MITK,RabadanLab/MITKats,fmilano/mitk,RabadanLab/MITKats,fmilano/mitk,RabadanLab/MITKats,MITK/MITK