[clang] [Clang] Add support for missing OpenCL extensions (PR #129777)

[Victor Mustya via cfe-commits]

vmustya wrote:

> What is the motivation for this change? We are trying to move away from adding extensions to this file for extensions that only add builtin functions, see e.g. https://reviews.llvm.org/D92231 . What functionality are you gaining by adding them here?

@svenvh, I'm trying to unify the extensions enablement in the user interface. We can enable or disable some of the extensions with the `-Xclang -cl-ext=+extension` command line options. For example, a user can pass `-Xclang -cl-ext=+cl_khr_subgroups` successfully, but the `-Xclang -cl-ext=+cl_khr_subgroup_ballot` has no effect on the compiler.

https://github.com/llvm/llvm-project/pull/129777