Do not compile, CMake Errors

[AndreyBronin]

• Wrong flex_lib submodule path.
• Some .cmake files is missing.

CMake Error at CMakeLists.txt:20 (include):
  include could not find load file:
    AddLLVM
CMake Error at CMakeLists.txt:21 (include):
  include could not find load file:
    ClangConfig
CMake Error at CMakeLists.txt:83 (add_llvm_executable):
  Unknown CMake command "add_llvm_executable".

[flexferrum]

Fast part of answer:

1. You need pre-built LLVM/clang 5.0 (not the recent release or upstream)
2. You should provide path to the LLVM installation/build via variables LLVM_INSTALL_ROOT
   This two preprequirements I'll describe in readme.md .

I have to check the problem with wrong flex_lib submodule path.

[flexferrum]

Seems like fixed. Needed second-hand check.

[AndreyBronin]

I checked the build on Ubuntu 16.04, it works fine But on 18.04 I had some issues with default llvm\clang versions and your cmake finders. I'll try to fix this issues and make matrix .travis.ci file

List of dependencies for build on Ubuntu 16.04 you can find in this Dockerfile

[flexferrum]

Thanks!