misc: Replace zero-length arrays with flexible array member (automatic)

Description copied from Linux kernel commit from Gustavo A. R. Silva
(see [3]):

--v-- description start --v--

  The current codebase makes use of the zero-length array language
  extension to the C90 standard, but the preferred mechanism to
  declare variable-length types such as these ones is a flexible
  array member [1], introduced in C99:

  struct foo {
      int stuff;
      struct boo array[];
  };

  By making use of the mechanism above, we will get a compiler
  warning in case the flexible array does not occur last in the
  structure, which will help us prevent some kind of undefined
  behavior bugs from being unadvertenly introduced [2] to the
  Linux codebase from now on.

--^-- description end --^--

Do the similar housekeeping in the QEMU codebase (which uses
C99 since commit 7be41675f7).

All these instances of code were found with the help of the
following Coccinelle script:

  @@
  identifier s, m, a;
  type t, T;
  @@
   struct s {
      ...
      t m;
  -   T a[0];
  +   T a[];
  };
  @@
  identifier s, m, a;
  type t, T;
  @@
   struct s {
      ...
      t m;
  -   T a[0];
  +   T a[];
   } QEMU_PACKED;

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=76497732932f
[3] https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/commit/?id=17642a2fbd2c1

Inspired-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

contrib/libvhost-user/libvhost-user.h

@@ -286,7 +286,7 @@ typedef struct VuVirtqInflight {
     uint16_t used_idx;
 
     /* Used to track the state of each descriptor in descriptor table */
-    VuDescStateSplit desc[0];
+    VuDescStateSplit desc[];
 } VuVirtqInflight;
 
 typedef struct VuVirtqInflightDesc {