libgo/testsuite: don't call kill without args

If the timeout subshell has no child processes,
    the "xargs | kill" will fail. Ensure there is
    some input for kill before calling it.
    
    Reviewed-on: https://go-review.googlesource.com/13295

From-SVN: r226719

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-6fb7c3509a4eda7d2403900981b53029d6727037
+5891a4c0615f469edcefc6d7a85a88984ba940aa
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/testsuite/gotest

@@ -518,7 +518,10 @@ xno)
 		wait $pid
 		status=$?
 		if ! test -f gotest-timeout; then
-		    ps -o pid,ppid | grep " $alarmpid" | cut -f1 -d" " | xargs kill -9
+		    out=`ps -o pid,ppid | grep " $alarmpid" | cut -f1 -d" "`
+		    if test "x$out" != "x"; then
+		        kill -9 $out
+		    fi
 		fi
 	else
 		if test "$trace" = "true"; then