Replace most gcc format attributes by macro GCC_FMT_ATTR (format checking)

Since version 4.4.x, gcc supports additional format attributes.
    __attribute__ ((format (gnu_printf, 1, 2)))
should be used instead of
    __attribute__ ((format (printf, 1, 2))
because QEMU always uses standard format strings (even with mingw32).

The patch replaces format attribute printf / __printf__ by macro
GCC_FMT_ATTR which uses gnu_printf if supported.

It also removes an #ifdef __GNUC__ (not needed any longer).

Cc: Blue Swirl <[email protected]>
Signed-off-by: Stefan Weil <[email protected]>
Signed-off-by: Blue Swirl <[email protected]>
diff --git a/qemu-error.h b/qemu-error.h
index a45609f..531ec63 100644
--- a/qemu-error.h
+++ b/qemu-error.h
@@ -31,11 +31,10 @@
 void loc_set_file(const char *fname, int lno);
 
 void error_vprintf(const char *fmt, va_list ap);
-void error_printf(const char *fmt, ...) __attribute__ ((format(printf, 1, 2)));
-void error_printf_unless_qmp(const char *fmt, ...)
-    __attribute__ ((format(printf, 1, 2)));
+void error_printf(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
+void error_printf_unless_qmp(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 void error_print_loc(void);
 void error_set_progname(const char *argv0);
-void error_report(const char *fmt, ...) __attribute__ ((format(printf, 1, 2)));
+void error_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 
 #endif