Reduce redundancy in utility functions

[mmoult]

Commit acfc25 introduced helpful utility functions to the C/C++ headers, but they have a lot of redundancy. These functions have long switch statements with trivial logic- ideal conditions for #defines. I did not see any style guide (perhaps the redundancy is unavoidable if #defines are forbidden), so I wrote this change.

Undoubtedly there are style considerations to do it the Khronos way. I figured I could submit this proposal and you can do with it what you will.

[CLAassistant]

All committers have signed the CLA.

[alan-baker]

These headers are all auto-generated. As it stands any future generation would override these changes. Take a look in the tools/buildHeaders directory for the code. I haven't thought too hard about the proposed changes themselves yet though.