API/ABI changes review for LLVM core libraries

The review of API/ABI changes for LLVM since version 3.6.2: https://abi-laboratory.pro/tracker/timeline/llvm/

Hope it will be helpful for users and maintainers of the library.

Created with the help of open-source abi-tracker tool: https://github.com/lvc/abi-tracker

## Environment
* Linux x86_64
* GCC 4.9
* LLVM 3.6.2 and higher

This is really cool! Thanks!

– Sean Silva

Very nice!