Simplified patch. Updated title and description

I'm running OpenCL on an x886 and everything is fine, but there are a lot of build bots which build different targets on different architectures. Since there are no target option specified, c-index-test uses native target.

If I understand correctly, not all extensions are available on non-x86 targets and some declarations are marked as (invalid) - that is the only difference I saw

Fixed issue in test/Index/opencl-types.cl

Rebased to ToT.

Updated opencl-c.h header: fixed typos in built-in declarations. Applied comment from Alexey

Applied comments. Rebased to ToT

Rebase to the ToT

Updated tests

@yaxunl could you please review this patch?

Removed unnecessary empty line from test

Added test

Updated tests. Reverted usage of #pragma OPENCL EXTENSION my_ext : begin due to a failed LIT tests: test/Headers/opencl-c-header.cl

Applied comments from Anastasia. Updated patch with more code unified

Applied comments from Anastasia. Updated headers to conform with the latest spec

This is an initial version. I guess there are some other enums related to CK_ZeroToOCL* which also can be merged.

Updated patch with new functionality and tests

Applied comment from Anastasia