Rationalize naming/access to current thread-local-storage scheme.  However, the preprocessor tokenizer is not thread-safe, so this may all change.

Also adding missing test.


git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@22249 e7fa87d3-cd2b-0410-9028-fcbf551c1848