error framework: Fix compilation for w32/w64

The declaration of function error_set() should use macro GCC_FMT_ATTR
instead of gcc's format printf attribute.

For w32/w64, both declarations are different and GCC_FMT_ATTR is needed.
Compilation for w64 even failed with the original code because mingw64
defines a macro for printf.

GCC_FMT_ATTR requires qemu-common.h, so add it in error.c
(it's also included by error_int.h but too late).

Remove assert.h which is included by qemu-common.h.

Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: NStefan Weil <weil@mail.berlios.de>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>

error.c

@@ -9,11 +9,12 @@
  * This work is licensed under the terms of the GNU LGPL, version 2.  See
  * the COPYING.LIB file in the top-level directory.
  */
+
+#include "qemu-common.h"
 #include "error.h"
 #include "error_int.h"
 #include "qemu-objects.h"
 #include "qerror.h"
-#include <assert.h>
 
 struct Error
 {

error.h

@@ -25,8 +25,7 @@ typedef struct Error Error;
  * Currently, qerror.h defines these error formats.  This function is not
  * meant to be used outside of QEMU.
  */
-void error_set(Error **err, const char *fmt, ...)
-    __attribute__((format(printf, 2, 3)));
+void error_set(Error **err, const char *fmt, ...) GCC_FMT_ATTR(2, 3);
 
 /**
  * Returns true if an indirect pointer to an error is pointing to a valid