gnu: Add texlive-zref-check.

* gnu/packages/tex.scm (texlive-zref-check): New variable.

gnu: Add texlive-ziffer.

* gnu/packages/tex.scm (texlive-ziffer): New variable.

gnu: Add texlive-zennote.

* gnu/packages/tex.scm (texlive-zennote): New variable.

gnu: Add texlive-zed-csp.

* gnu/packages/tex.scm (texlive-zed-csp): New variable.

gnu: Add texlive-zebra-goodies.

* gnu/packages/tex.scm (texlive-zebra-goodies): New variable.

gnu: Add texlive-yplan.

* gnu/packages/tex.scm (texlive-yplan): New variable.

gnu: Add texlive-ycbook.

* gnu/packages/tex.scm (texlive-ycbook): New variable.

gnu: Add texlive-yaletter.

* gnu/packages/tex.scm (texlive-yaletter): New variable.

gnu: Add texlive-yagusylo.

* gnu/packages/tex.scm (texlive-yagusylo): New variable.

gnu: Add texlive-yafoot.

* gnu/packages/tex.scm (texlive-yafoot): New variable.

gnu: Add texlive-xytree.

* gnu/packages/tex.scm (texlive-xytree): New variable.

gnu: Add texlive-xwatermark.

* gnu/packages/tex.scm (texlive-xwatermark): New variable.

gnu: Add texlive-xurl.

* gnu/packages/tex.scm (texlive-xurl): New variable.

gnu: Add texlive-xtab.

* gnu/packages/tex.scm (texlive-xtab): New variable.

gnu: Add texlive-xsim.

* gnu/packages/tex.scm (texlive-xsim): New variable.

gnu: Add texlive-xsavebox.

* gnu/packages/tex.scm (texlive-xsavebox): New variable.

gnu: Add texlive-xprintlen.

* gnu/packages/tex.scm (texlive-xprintlen): New variable.

gnu: Add texlive-xpeek.

* gnu/packages/tex.scm (texlive-xpeek): New variable.

gnu: Add texlive-xpunctuate.

* gnu/packages/tex.scm (texlive-xpunctuate): New variable.

gnu: Add texlive-xoptarg.

* gnu/packages/tex.scm (texlive-xoptarg): New variable.