Fix compiler warning in linux-namespaces.c

../../gdb/nat/linux-namespaces.c: In function ‘void mnsh_main(int)’:
../../gdb/nat/linux-namespaces.c:604:8: warning: ‘fd’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  close (fd);
  ~~~~~~^~~~

And the warning is correct -- mnsh_recv_message can return -1 and leave fd
uninitialized, and mnsh_main will still call close (fd) if that happens.

Initialize fd to -1 to avoid that.

gdb/ChangeLog:

2019-08-27  Christian Biesinger  <cbiesinger@google.com>

	* nat/linux-namespaces.c (mnsh_main): Initialize fd (to -1).

1 files changed, 1 insertions, 1 deletions

diff --git a/gdb/nat/linux-namespaces.c b/gdb/nat/linux-namespaces.c
index 503f755..e49bc1a 100644
--- a/gdb/nat/linux-namespaces.c
+++ b/gdb/nat/linux-namespaces.c
@@ -562,7 +562,7 @@ mnsh_main (int sock)
   while (1)
     {
       enum mnsh_msg_type type;
-      int fd, int1, int2;
+      int fd = -1, int1, int2;
       char buf[PATH_MAX];
       ssize_t size, response = -1;