Add fprintf_function for function pointers to fprintf-like functions

This kind of function pointers is used very often in qemu.

The new data type uses format checking with GCC_FMT_ATTR
and will be used in later patches.

Cc: Blue Swirl <blauwirbel@gmail.com>
Signed-off-by: NStefan Weil <weil@mail.berlios.de>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

qemu-common.h

@@ -81,6 +81,9 @@ struct iovec {
 #define GCC_FMT_ATTR(n, m)
 #endif
 
+typedef int (*fprintf_function)(FILE *f, const char *fmt, ...)
+    GCC_FMT_ATTR(2, 3);
+
 #ifdef _WIN32
 #define fsync _commit
 #define lseek _lseeki64