w32: Always use standard instead of native format strings

GLib 2.0 include files use __printf__ for the format attribute
which resolves to native format strings on w32 hosts.

QEMU wants standard format strings instead of native format
strings, so we simply change any declaration with __printf__
to use __gnu_printf__.

This works because all basic printf functions support both
kinds of format strings.

This fixes a compiler warning:

qapi/string-output-visitor.c: In function ‘print_type_int’:
qapi/string-output-visitor.c:34:5: warning: unknown conversion type character ‘l’ in format [-Wformat]
qapi/string-output-visitor.c:34:5: warning: too many arguments for format [-Wformat-extra-args]
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NStefan Hajnoczi <stefanha@gmail.com>

compiler.h

@@ -44,6 +44,11 @@
    /* Use gnu_printf when supported (qemu uses standard format strings). */
 #  define GCC_ATTR __attribute__((__unused__, format(gnu_printf, 1, 2)))
 #  define GCC_FMT_ATTR(n, m) __attribute__((format(gnu_printf, n, m)))
+#  if defined(_WIN32)
+    /* Map __printf__ to __gnu_printf__ because we want standard format strings
+     * even when MinGW or GLib include files use __printf__. */
+#   define __printf__ __gnu_printf__
+#  endif
 # endif
 #if defined(_WIN32)
 #define GCC_WEAK __attribute__((weak))