Bring order to the OpenCL keywords

Avoid the gratuitous repurposing of C++ keyword 'private' by using a keyword
alias.

Also attempt to document the OpenCL keywords based on scraps of information
found online.

The purpose of this commit is to reduce impact on the C++ parser.
[lsan] Remove the LSan-specific verbosity flag.

It conflicted with the verbosity flag we had in common flags. We don't need an
LSan-specific flag anyway.

Also, shift some logging levels and remove some unnecessary code.