Per the comment, we cannot rely on bsd.own.mk

we could be on an old system that knows noting of MK_BMAKE
or on an almost up to date one that is defaulting it to "no"
neither of which will work.

usr.bin/bmake/Makefile.inc

@@ -1,12 +1,5 @@
 # $FreeBSD$ 
 
-# we need the up to date bsd.own.mk
-.if ${.CURDIR:M*make} == ""
-.sinclude "share/mk/bsd.own.mk"
-.else
-.sinclude "../../share/mk/bsd.own.mk"
-.endif
-# the above should have found it...
 .include "bsd.own.mk"
 
 .if defined(.PARSEDIR)
@@ -14,6 +7,12 @@
 .export SRCTOP
 .endif
 
+# Sadly, we cannot assume bsd.own.mk did its job,
+# nor can we safely include the one we want
+.if !defined(WITHOUT_BMAKE)
+MK_BMAKE= yes
+.endif
+
 .if defined(MK_BMAKE) && ${MK_BMAKE} != "no"
 PROG= make
 .endif