pipe should not be a reserved keyword for OpenCL versions prior to 2.0

The unified spec doesn't seem to say that pipe is a reserved keyword from OpenCL 2.0 onwards.
https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/OpenCL_C.html#keywords

But if I look at the older version specs it is indeed not listed there.

https://www.khronos.org/registry/OpenCL/specs/opencl-1.2.pdf

Btw I believe the same applies to `__generic`.

Compare the OpenCL C 3.0 unified specification keyword section with the linked OpenCL 1.2 PDF, checking the reported treatment of `pipe` and `__generic`. Locate the corresponding source entry in this repository and verify that the documented keyword rules match the applicable OpenCL versions; done means the specification is corrected and the affected versions are unambiguous.

Written by the indexing model from the issue text.