Which compilers, compiler options, and C/C++ standard versions do the headers support?

We haven't documented which compilers and compiler options including C and C++ standard versions the headers support, which makes it difficult to determine if issues like #115 and #121 are header issues or unsupported configurations. We should document (and test for!) the compilers and compiler options we're intending to support and be clear that other configurations may not work or have limitations.

FWIW, there is a similar issue already for the C++ bindings:
https://github.com/KhronosGroup/OpenCL-CLHPP/issues/78

No files or tests are named. Start by locating the project’s current compiler and standard-version checks, then inventory the intended compiler options and supported C/C++ standards. Done means the supported configurations are documented, unsupported configurations are clearly qualified, and automated coverage tests them.

Written by the indexing model from the issue text.