[helpers] YCM helper

YouCompleteMe helper, updates the YCM config file once YCM-Generator
creates one for you. The steps are:

 * Install YCM / Generator
 * Inside Vim, on $LLVM_SRC, run :YcmGenerateConfig
 * Outside vim, with llvm-env on the same workdir run: llvm-ycm
 * Re-start vim, all is good

Why is this needed?

 1. YCM relies on .ycm_extra_conf.py to be precise and correct
 2. LLVM includes headers and libraries from both source and build dirs
 3. YCM-Generator has no idea about the build dir, so it uses /tmp

Note:

 * You will need to do this for each workdir, as the path has to be absolute
 * Don't use CMake's compilation_database.json, or header files won't work

Change-Id: If14008d96d7198060cb403439db55c234693c837
1 file changed