bmake[1]: don't know how to make _bootstrap-tools-usr.bin/m4. Stop

[Slawa Olhovchenkov]

I am try to upgrade very old 10-CURRENT to latest 10-STABLE and got
next error:

===> usr.bin/yacc (obj,depend,all,install)
bmake[1]: don't know how to make _bootstrap-tools-usr.bin/m4. Stop

bmake[1]: stopped in /usr/src
*** Error code 2

Stop.
bmake: stopped in /usr/src
*** [buildworld] Error code 1

Stop in /usr/src.