GitLab

Depends on xdg-email being available.

* lisp/mail/emacsbug.el (report-emacs-bug-insert-to-mailer)
(report-emacs-bug-can-use-xdg-email): New functions.
(report-emacs-bug): Set can-xdg-email to result of
report-emacs-bug-can-use-xdg-email.  If can-xdg-email bind
\C-cm to report-emacs-bug-insert-to-mailer and add help text
about it.