fix latexmk not using xetex

[Honigmelone]

Fix latexmk working with xetex

Hi, i dont know if my problem is universal but I fixed it and this was my solution. Feel free to edit or anything. I previously used this emacs configuration: https://github.com/basille/.emacs.d/ where latexmk works with xetex. By comparing the configurations I came up with this solution. Why it works with this change is black magic to me.

Problem Description:
When editing an xetex document in auctex LatexMk chooses pdflatex and fails.
How to reproduce:

1. create xelatex document with the following content:

\documentclass{article}
\usepackage{fontspec}
\begin{document}
This is a unicode Test: Ä
\end{document}
%%% Local Variables:
%%% coding: utf-8
%%% mode: latex
%%% TeX-engine: xetex
%%% TeX-master: t
%%% End:

2. Press C-c C-c and choose Latexmk as command

Observed behaviour: 👀 💔

ERROR: Fatal fontspec error: "cannot-use-pdftex"

--- TeX said ---
! 
! The fontspec package requires either XeTeX or LuaTeX to function.
! 
Observed behaviour: :eyes: :broken_heart:
ERROR: Fatal fontspec error: "cannot-use-pdftex"

--- TeX said ---
! 
! The fontspec package requires either XeTeX or LuaTeX to function.
! 
! You must change your typesetting engine to, e.g., "xelatex" or "lualatex"
! instead of plain "latex" or "pdflatex".
! 
! See the fontspec documentation for further information.
! 
! For immediate help type H <return>.
!...............................................  

l.41  }

--- HELP ---
No help available

Expected behavior:
LaTeX: successfully formatted {1} page

[TheBB]

I appreciate the help but this can't be the solution. First it loads a package on startup, which we must avoid, second there is already code to load the package when tex loads. Does (featurep 'auctex-latexmk) evaluate to false in a tex file?

[Honigmelone]

It evaluates to t no matter if i reload latexmk or not.

[github-actions]

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