To make it clear how silly this debate is. Substitue GLSL for say, gcc, llvm, python, lua, Java, gdb or any other even moderatly popular system of programming/compiling/debugging things. All of the former (and most of the ones implied) have a structured way to communicate errors so they're fit for machine consumption.
The only place I've seen the untenable position of not having a structured way to do it being discussed in earnest, is here and in ES-discuss (on JS stack traces). I cannot believe it honestly. You understand how this is a mystery to me right?