Link against libclang-cpp.so when linking with shared libraries
Link against libclang-cpp.so when linking with shared libraries

libclang-cpp.so is a new shared object in clang-9.0.0 which
contains all the clang components in one library.  Doing this will
save us from having to update cmake when there is a new clang component
and may provide better performance in LTO builds of clang.

pocl/pocl,franz/pocl,pocl/pocl,Oblomov/pocl,Oblomov/pocl,franz/pocl,Oblomov/pocl,Oblomov/pocl,Oblomov/pocl,franz/pocl,pocl/pocl,franz/pocl,pocl/pocl,franz/pocl,pocl/pocl