Revert "No need to link libclang into kdevclangsupport"

Cough, this caused a FTBFS. kdevclangsupport (better: clangparsejob.cpp)
still needs symbols from libclang.

Can't think of a better solution at the moment. In fact we should
probably disallow using a static libclang library altogether.

This reverts commit c1eba8fc7983a5f553b28d57a1ad3cea956c0aae.