Not all Pmake derivatives silently handle empty shell output, so ensure there

is something for make(1) to consume.  Bmake gives output such as:
   "warning: Couldn't read shell's output for "/bin/sh -c true"
Note we parted from traditional Pmake behavior in r18864 / r18255.

Makefile

@@ -216,7 +216,7 @@ ${TGTS}:
 .MAIN:	all
 
 STARTTIME!= LC_ALL=C date
-CHECK_TIME!= find ${.CURDIR}/sys/sys/param.h -mtime -0s
+CHECK_TIME!= find ${.CURDIR}/sys/sys/param.h -mtime -0s ; echo
 .if !empty(CHECK_TIME)
 .error check your date/time: ${STARTTIME}
 .endif

Makefile.inc1

@@ -1558,7 +1558,7 @@ DTBOUTPUTPATH= ${KRNLOBJDIR}/${KERNCONF}/
 .if !defined(FDT_DTS_FILE) || empty(FDT_DTS_FILE)
 .if exists(${KERNCONFDIR}/${KERNCONF})
 FDT_DTS_FILE!= awk 'BEGIN {FS="="} /^makeoptions[[:space:]]+FDT_DTS_FILE/ {print $$2}' \
-	${KERNCONFDIR}/${KERNCONF}
+	${KERNCONFDIR}/${KERNCONF} ; echo
 .endif
 .endif