Compile llvm and clang with RTTI

[pfernique]

Could it be possible to modify the llvm-compilers-feedstock/recipe/build.sh to add the option _cmake_config+=(-DLLVM_ENABLE_RTTI:BOOL=ON) ?
This would enable RTTI on llvm and clang libraries.
I know it is not standard, but to construct PyBind11 or Boost.Python wrappers of Clang, this is mandatory.
This is used in the ClangLite for AutoWIG, an automatic C++/Python binding generator based on Clang generated ASTs.