Construct an XDOC tree for a generated definition directive @(gdef ...).
Macro:
(defmacro @gdef (&rest trees) (list '@gdef-fn (cons 'list trees)))
Function:
(defun @gdef-fn (trees) (declare (xargs :guard (tree-listp trees))) (make-tree-dir/&& :@gdef trees))
Theorem:
(defthm stringp-of-@gdef (equal (treep (@gdef-fn trees)) (tree-listp trees)))