Simplify location of bootstrap make.

Sponsored by:	Dell EMC Isilon

Makefile

@@ -209,7 +209,7 @@ WANT_MAKE_VERSION= 20160604
 # 20160220 - support .dinclude for FAST_DEPEND.
 WANT_MAKE_VERSION= 20160220
 .endif
-MYMAKE=		${MAKEOBJDIRPREFIX}${.CURDIR}/make.${MACHINE}/${WANT_MAKE}
+MYMAKE=		${OBJROOT}make.${MACHINE}/${WANT_MAKE}
 .if defined(.PARSEDIR)
 HAVE_MAKE=	bmake
 .else
@@ -407,10 +407,13 @@ upgrade_checks: .PHONY
 # headers, libraries and tools.  Also, allow the location of
 # the system bsdmake-like utility to be overridden.
 #
-MMAKEENV=	MAKEOBJDIRPREFIX=${MYMAKE:H} \
+MMAKEENV=	\
 		DESTDIR= \
 		INSTALL="sh ${.CURDIR}/tools/install.sh"
 MMAKE=		${MMAKEENV} ${MAKE} \
+		OBJTOP=${MYMAKE:H}/obj \
+		OBJROOT='$${OBJTOP}/' \
+		MAKEOBJDIRPREFIX= \
 		MAN= -DNO_SHARED \
 		-DNO_CPU_CFLAGS -DNO_WERROR \
 		-DNO_SUBDIR \