DIRDEPS_BUILD: Don't hook 'beforebuild' into 'all' in MAKELEVEL 0.

This was a mistake in r295641, but is effectively prevented from
being a problem due to r296699 preventing 'make all' from being
usable at MAKELEVEL 0 for DIRDEPS_BUILD.

MFC after:	2 weeks
Sponsored by:	Dell EMC Isilon

share/mk/bsd.init.mk

@@ -15,10 +15,6 @@ __<bsd.init.mk>__:
 .endif
 .include <bsd.own.mk>
 .MAIN: all
-beforebuild: .PHONY .NOTMAIN
-.if !defined(_SKIP_BUILD)
-all: beforebuild .WAIT
-.endif
 
 .if ${.MAKE.LEVEL:U1} == 0 && ${BUILD_AT_LEVEL0:Uyes:tl} == "no" && !make(clean*)
 # this tells lib.mk and prog.mk to not actually build anything
@@ -28,6 +24,11 @@ _SKIP_BUILD = not building at level 0
 .warning ${_SKIP_BUILD}
 .endif
 
+beforebuild: .PHONY .NOTMAIN
+.if !defined(_SKIP_BUILD)
+all: beforebuild .WAIT
+.endif
+
 .if ${MK_META_MODE} == "yes"
 .if !exists(/dev/filemon) && \
     ${UPDATE_DEPENDFILE:Uyes:tl} != "no" && !defined(NO_FILEMON) && \