nir/clone: Export nir_variable_clone

Reviewed-by: Rob Clark <robclark@gmail.com>

src/compiler/nir/nir.h

@@ -2052,6 +2052,7 @@ void nir_print_instr(const nir_instr *instr, FILE *fp);
 nir_shader *nir_shader_clone(void *mem_ctx, const nir_shader *s);
 nir_function_impl *nir_function_impl_clone(const nir_function_impl *fi);
 nir_constant *nir_constant_clone(const nir_constant *c, nir_variable *var);
+nir_variable *nir_variable_clone(const nir_variable *c, nir_shader *shader);
 
 #ifdef DEBUG
 void nir_validate_shader(nir_shader *shader);