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

[Victor Mustya via cfe-commits]

vmustya wrote:

> That way, header-only extensions don't need to be added to `OpenCLExtensions.def`

@svenvh, in any case, we need a list of all the supported extensions, including the header ones. When someone passes the `-Xclang -cl-ext=+all`, the compiler should add defines for all the supported extensions.

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