Missing GL thunk function definitions
```
template<> struct fex_gen_config<glGetVkProcAddrNV> {};
template<> struct fex_gen_config<glPathColorGenNV> {};
template<> struct fex_gen_config<glPathTexGenNV> {};
template<> struct fex_gen_config<glPathFogGenNV> {};
template<> struct fex_gen_config<glGetPathColorGenivNV> {};
template<> struct fex_gen_config<glGetPathColorGenfvNV> {};
template<> struct fex_gen_config<glGetPathTexGenivNV> {};
template<> struct fex_gen_config<glGetPathTexGenfvNV> {};
template<> struct fex_gen_config<glBlendEquationSeparateATI> {};
```

Only a few missing but not sure how `glGetVkProcAddrNV` will work for us.