Use AC_HEADER_MAJOR

Instead of checking for sys/mkdev.h headerfile, there is the
AC_HEADER_MAJOR helper for how to get major(), minor(), makedev().

https://bugzilla.gnome.org/show_bug.cgi?id=712314

gio/gdbusmessage.c

@@ -29,13 +29,16 @@
 #include <errno.h>
 #include <sys/types.h>
 #include <sys/stat.h>
-#ifdef HAVE_SYS_MKDEV_H
-#include <sys/mkdev.h>
-#endif
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
 #endif
 
+#if MAJOR_IN_MKDEV
+#include <sys/mkdev.h>
+#elif MAJOR_IN_SYSMACROS
+#include <sys/sysmacros.h>
+#endif
+
 #include "gdbusutils.h"
 #include "gdbusmessage.h"
 #include "gdbuserror.h"