this avoids problems in the latest version of latexmk where the $pdflatex variable has been replaced by $xelatex and $lualatex when running with -xelatex or -lualatex
this avoids problems in the latest version of latexmk where the $pdflatex variable has been replaced by $xelatex and $lualatex when running with -xelatex or -lualatex