Cygwin: proc: return more useful cmdline

Creating /proc/<PID>/cmdline requires permissions to communicate
with the target process via its signal pipe.  If that fails, the
output is "<defunct>" which doesn't make sense most of the time.
Rather, call format_process_exename in this case to get more useful
process name info, albeit not the full cmdline.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/fhandler_process.cc

@@ -519,12 +519,9 @@ format_process_cmdline (void *data, char *&destbuf)
       destbuf = NULL;
     }
   destbuf = p ? p->cmdline (fs) : NULL;
-  if (!destbuf || !*destbuf)
-    {
-      destbuf = cstrdup ("<defunct>");
-      fs = strlen (destbuf) + 1;
-    }
-  return fs;
+  if (destbuf && *destbuf)
+    return fs;
+  return format_process_exename (data, destbuf);
 }
 
 static off_t