update linking to use libclang-cpp.so instead of libclangBasic.so

[jperrin]

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 from having to update cmake when there is a new clang component
and may provide better performance in LTO builds of clang.

[MarioHewardt]

This is a BCC dependency and not procmon.