Log Message:
texlive: update to TeXLive 2021

General:
* Donald Knuth’s changes for his 2021 tuneup of TeX and Metafont are
  incorporated (https://tug.org/TUGboat/tb42-1/tb130knuth-tuneup21.pdf). They
  are also available on CTAN as the knuth-dist and knuth-local packages. As
  expected, the fixes are for obscure cases and do not affect any behavior in
  practice.
* Except in original TeX: if \tracinglostchars is set to 3 or more, missing
  characters will result in an error, not just a message in the log file, and
  the missing character code will be shown in hex.
* Except in original TeX: a new integer parameter \tracingstacklevels, if
  positive, and \tracingmacros is also positive, causes a prefix indicating the
  macro expansion depth to be output on each relevant log line (e.g., ~.. at
  depth 2). Also, macro logging is truncated at a depth ≥ the parameter value.

Aleph: The Aleph-based LaTeX format, named lamed, has been removed. The aleph
  binary itself is still included and supported.

LuaTeX:
* Lua 5.3.6.
* Callback for nesting level used in \tracingmacros, as generalized variant
  of the new \tracingstacklevels.
* Mark math glyphs as protected to prevent processing as text.
* Removed width/ic compensation for traditional math code path.

MetaPost:
* SOURCE_DATE_EPOCH environment variable support for reproducible output.
* Avoid wrong final % in mpto.
* Document -T option, other fixes to manual.
* Value of epsilon changed in binary and decimal modes, so mp_solve_rising_cubic
  works as expected.

pdfTeX:
* New primitives \pdfrunninglinkoff and \pdfrunninglinkon; e.g., for
  disabling generation of links in headers and footers.
* Warn instead of aborting when “\pdfendlink ended up in different nesting
  level than \pdfstartlink”.
* Dump \pdfglyphtounicode assignments in fmt file.
* Source: poppler support removed, as it was too hard to keep in sync with
  upstream. In native TL, pdfTeX has always used libs/xpdf, which is cut-down
  and adapted code from xpdf.

XeTeX: Fixes for math kerning.

Dvipdfmx:
* Ghostscript is now invoked safely by default; to override (assuming all
  input files are trusted), use -i dvipdfmx-unsafe.cfg. To use PSTricks with
  XeTeX, this is required, as in:
   xetex -output-driver="xdvipdfmx -i dvipdfmx-unsafe.cfg -q -E" ...
* If an image file is not found, exit with bad status.
* Extended special syntax for color support.
* Specials for manipulating ExtGState.
* Compatibility specials pdfcolorstack and pdffontattr.
* Experimental support for dviluatex’s extended fnt_def.
* Support new feature of virtual font to fallback Japanese font definition.

Dvips:
* Default PostScript document title is now the basename of the input file,
  and can be overridden with the new option -title.
* If an .eps or other image file is not found, exit with bad status.
* Support new feature of virtual font to fallback Japanese font definition.