Generate tests that use all definitions provided by the headers

We currently have automated testing in place for a good numbers of compilers, C versions, etc but the test code we're compiling uses almost none of the definitions provided by the headers which means there are a lot of warnings/errors we're not currently seeing in automated testing (see https://github.com/KhronosGroup/OpenCL-Headers/pull/187 for an example). We should generate tests from the spec XML that use all the definitions provided by the headers.

Review the existing automated test code and the spec XML referenced in the issue, then compare them with the definitions exposed by the headers. Use pull request #187 as the concrete example of currently missed warnings or errors. Done means generated tests exercise all definitions provided by the headers across the supported compilers and C versions.

Written by the indexing model from the issue text.