glsl: Save and restore the whole switch state for nesting.

This stuffs them all in a struct for sanity.  Fixes piglit
glsl-1.30/execution/switch/fs-uniform-nested.

NOTE: This is a candidate for the 8.0 branch.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/glsl_parser_extras.cpp

@@ -51,7 +51,7 @@ _mesa_glsl_parse_state::_mesa_glsl_parse_state(struct gl_context *ctx,
    this->info_log = ralloc_strdup(mem_ctx, "");
    this->error = false;
    this->loop_nesting_ast = NULL;
-   this->switch_nesting_ast = NULL;
+   this->switch_state.switch_nesting_ast = NULL;
 
    this->num_builtins_to_link = 0;