Bug#848368: llvm-toolchain-3.9: Please add ELF symbols versions to the libraries

[Rebecca N. Palmer]

The patches in SVN have a bug: 4.0 is using LLVM_3.9 for libllvm 
(simple_version_script.map), though the correct LLVM_4.0 elsewhere 
(AddLLVM.cmake).

The override_dh_makeshlibs/1:x symbols minimum version are needed in all 
versions, not just 3.8.

> Also, #857623 (the OpenCL bug) also affects 3.8 and 4.0; the same fix
> should work.
This has not yet been done.