libvchan: address compiler warnings

Both vchan_wr() and stdout_wr() should be defined with a non-empty
argument list (i.e. void). Additionally both of them as well as usage()
should be static to make clear that no other code is referencing them.

Further, statements should follow declarations.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/tools/libvchan/node-select.c
+++ b/tools/libvchan/node-select.c
@@ -39,7 +39,7 @@
 
 #include <libxenvchan.h>
 
-void usage(char** argv)
+static void usage(char** argv)
 {
 	fprintf(stderr, "usage:\n"
 		"\t%s [client|server] domainid nodepath [rbufsiz wbufsiz]\n",
@@ -54,10 +54,12 @@ int insiz = 0;
 int outsiz = 0;
 struct libxenvchan *ctrl = 0;
 
-void vchan_wr() {
+static void vchan_wr(void) {
+	int ret;
+
 	if (!insiz)
 		return;
-	int ret = libxenvchan_write(ctrl, inbuf, insiz);
+	ret = libxenvchan_write(ctrl, inbuf, insiz);
 	if (ret < 0) {
 		fprintf(stderr, "vchan write failed\n");
 		exit(1);
@@ -68,10 +70,12 @@ void vchan_wr() {
 	}
 }
 
-void stdout_wr() {
+static void stdout_wr(void) {
+	int ret;
+
 	if (!outsiz)
 		return;
-	int ret = write(1, outbuf, outsiz);
+	ret = write(1, outbuf, outsiz);
 	if (ret < 0 && errno != EAGAIN)
 		exit(1);
 	if (ret > 0) {