editors/emacs-devel: Update to pull in new concurrency features.

• Minimize the differences with editors/emacs.
• Do not require GCC to work around a clang bug. The OS versions for which this was relevant are no longer supported.
• The check for X11 is handled with the X11 option and _IMPLIES, so remove the redundant .if logic.

Approved by: swills (mentor) asish (maintainer)
Differential Revision: https://reviews.freebsd.org/D8796