Pull up following revision(s) (requested by tsutsui in ticket #40):

sys/arch/mac68k/conf/INSTALL: revision 1.58

Disable (comment out) options DIAGNOSTIC in INSTALL kernels.

It has been there since the initial revision 1.1 while
it was disabled in GENERIC in revision 1.121 back in 2002.

Briefly discussed in PR/57107

(martin)