The Hershey fonts are now stored in a portable binary format and are kept
in ../data/plstnd5.fnt (standard fonts) and ../data/plxtnd5.fnt (extended
fonts).

If you really must rebuild the font files, you can do so using the
font??.c, stndfont.c, and xtndfont.c source code files in this directory.
Just add the -DBUILD_HERSHEY_FONTS=ON option to the cmake command line, and
do the normal PLplot build in the build tree.  Then cd to the fonts directory
in the build tree and run

./generate_stndfonts; ./generate_xtndfonts

This will create the standard and extended Hershey fonts in binary form as
plstnd5.fnt and plxtnd5.fnt.  Then compare them with the ones already in
the source tree data directory to confirm no changes have occurred.  (AWI
last did this check on 2016-07-17 after making some substantial changes
to stndfont.c, and xtndfont.c to get rid of compiler warnings).
