run-command.c: fix build warnings on Ubuntu

Building git on Ubuntu 9.10 warns that the return value of write(2)
isn't checked. These warnings were introduced in commits:

  2b541bf8 ("start_command: detect execvp failures early")
  a5487ddf ("start_command: report child process setup errors to the
parent's stderr")

GCC details:

  $ gcc --version
  gcc (Ubuntu 4.4.1-4ubuntu9) 4.4.1

Silence the warnings by reading (but not making use of) the return value
of write(2).

Signed-off-by: Michael Wookey <michaelwookey@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

run-command.c

@@ -67,19 +67,21 @@ static int child_notifier = -1;
 
 static void notify_parent(void)
 {
-	write(child_notifier, "", 1);
+	ssize_t unused;
+	unused = write(child_notifier, "", 1);
 }
 
 static NORETURN void die_child(const char *err, va_list params)
 {
 	char msg[4096];
+	ssize_t unused;
 	int len = vsnprintf(msg, sizeof(msg), err, params);
 	if (len > sizeof(msg))
 		len = sizeof(msg);
 
-	write(child_err, "fatal: ", 7);
-	write(child_err, msg, len);
-	write(child_err, "\n", 1);
+	unused = write(child_err, "fatal: ", 7);
+	unused = write(child_err, msg, len);
+	unused = write(child_err, "\n", 1);
 	exit(128);
 }