I got a different one this time:
~/tinymux/mux/src$ make depend
g++ -g -O -DSTUB_SLAVE -DINLINESQL -I/usr/include/mysql -c unsplit.cpp
g++ -g -O -DSTUB_SLAVE -DINLINESQL -I/usr/include/mysql -o unsplit unsplit.o
for i in _build.cpp alarm.cpp alloc.cpp attrcache.cpp boolexp.cpp bsd.cpp command.cpp comsys.cpp conf.cpp cque.cpp create.cpp db.cpp db_rw.cpp eval.cpp file_c.cpp flags.cpp funceval.cpp funceval2.cpp functions.cpp funmath.cpp game.cpp help.cpp htab.cpp local.cpp log.cpp look.cpp mail.cpp match.cpp mathutil.cpp mguests.cpp modules.cpp move.cpp muxcli.cpp netcommon.cpp object.cpp predicates.cpp player.cpp player_c.cpp plusemail.cpp powers.cpp quota.cpp rob.cpp pcre.cpp set.cpp sha1.cpp speech.cpp stringutil.cpp strtod.cpp svdrand.cpp svdhash.cpp timer.cpp timeabsolute.cpp timedelta.cpp timeparser.cpp timeutil.cpp timezone.cpp unparse.cpp utf8tables.cpp vattr.cpp walkdb.cpp wild.cpp wiz.cpp libmux.cpp version.cpp unsplit.cpp slave.cpp stubslave.cpp ; do g++ -E -g -O -DSTUB_SLAVE -DINLINESQL -I/usr/include/mysql -M $i; done | ./unsplit > .depend~
functions.cpp:26:10: fatal error: mysql.h: No such file or directory
#include <mysql.h>
^~~~~~~~~
compilation terminated.
game.cpp:30:10: fatal error: mysql.h: No such file or directory
#include <mysql.h>
^~~~~~~~~
compilation terminated.
Makefile:207: recipe for target 'depend' failed
make: *** [depend] Error 1