[OpenCL] Add support of language builtins for OpenCL C 3.0

OpenCL C 3.0 introduces optionality to some builtins, in particularly
to those which are conditionally supported with pipe, device enqueue
and generic address space features.

The idea is to conditionally support such builtins depending on the language options
being set for a certain feature. This allows users to define functions with names
of those optional builtins in OpenCL (as such names are not reserved).

Reviewed By: Anastasia

Differential Revision: https://reviews.llvm.org/D118605