A small thing.  But I prefer this as Linker rather than SpirvLinker.   We already know it's SPIR-V because of the namespace.  That would also be more in line with what's in optimizer.hpp. There we just have "Optimizer"    SpirvTools in libspirv.hpp is kind of special since it mirrors what's in the C header file libspirv.h.  That's my excuse. :-)