Move all the headers CTS tests to this repository?

[kpet]

There are a number of so-called "headers" tests in the CTS (https://github.com/KhronosGroup/OpenCL-CTS/tree/master/test_conformance/headers) that don't really test the OpenCL implementation itself but rather whether the headers build cleanly using the target toolchain and whether some aspects of them behave correctly.

I think these tests should be moved to the headers repo as they're effectively testing the headers in isolation. However, I still see value in requiring that these tests pass on a platform for which OpenCL compliance is sought. Maybe this can be a requirement of the conformance process?

Any opinions?