glsl: Don't allow invalid identifiers as struct names.

Fixes piglit test
spec/glsl-1.10/compiler/struct/struct-name-uses-gl-prefix.vert.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/ast_to_hir.cpp

@@ -4575,6 +4575,8 @@ ast_struct_specifier::hir(exec_list *instructions,
                                                false,
                                                false /* allow_reserved_names */);
 
+   validate_identifier(this->name, loc, state);
+
    const glsl_type *t =
       glsl_type::get_record_instance(fields, decl_count, this->name);