WITH_META_MODE: Avoid "building" .depend if there is nothing to do.

This avoids 'Building /path/.depend' when it will not actually produce a
file.

Sponsored by:	EMC / Isilon Storage Division

share/mk/bsd.dep.mk

@@ -246,7 +246,9 @@ DPSRCS+= ${SRCS}
 # beforedepend/_EXTRADEPEND/afterdepend.  The target is kept
 # to allow 'make depend' to generate files.
 ${DEPENDFILE}: ${DPSRCS}
-.if !empty(.MAKE.MODE:Mmeta) || exists(${.OBJDIR}/${DEPENDFILE})
+.if exists(${.OBJDIR}/${DEPENDFILE}) || \
+    ((commands(beforedepend) || commands(_EXTRADEPEND) || \
+    commands(afterdepend)) && !empty(.MAKE.MODE:Mmeta))
 	rm -f ${DEPENDFILE}
 .endif
 .if target(_EXTRADEPEND)