I am a bit confused as to where Spir-V will be on the stack with relation to GLSL. By looking at the presentation it looked as though you might be able to compile GLSL as a front end to SPIR-V but seems like its being done the other way around https://code.google.com/p/lunarglass/source/detail?r=1061 .
What LunarGlass does with SPIR-V has nothing to do with the intent of the language. But more importantly, note the comment in the commit description: “SPIR-V -> Top IR. Add SPIR-V front end, generated from glslang.”
LunarGlass has its own IR language (Top IT). Their way of handling SPIR-V therefore is to convert it into Top IR. Thus, from their perspective, they have a SPIR-V front-end. But even then, their GLSL generates the SPIR-V, which is converted into Top IR.