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

[Sven van Haastregt via cfe-commits]

svenvh wrote:

> When someone passes the `-Xclang -cl-ext=+all`, the compiler should add defines for all the supported extensions.

Indeed; we already have such a list in `opencl-c-base.h` to enable all header-only extensions for the `spir`/`spirv` targets, so it should be easy to make `-cl-ext=+all` also enable those defines.

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