osdep.h: Define macros for the benefit of C++ before C++11

For C++ before C++11, <stdint.h> requires definition of the macros
__STDC_CONSTANT_MACROS, __STDC_LIMIT_MACROS and __STDC_FORMAT_MACROS
in order to enable definition of various macros by the header file.
Define these in osdep.h, so that we get the right header file
definitions whether osdep.h is being used by plain C, C++11 or
older C++.

In particular libvixl's header files depend on this and won't
compile if osdep.h is included before them otherwise.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NEric Blake <eblake@redhat.com>

include/qemu/osdep.h

@@ -28,6 +28,20 @@
 #include "config-host.h"
 #include "qemu/compiler.h"
 
+/* Older versions of C++ don't get definitions of various macros from
+ * stdlib.h unless we define these macros before first inclusion of
+ * that system header.
+ */
+#ifndef __STDC_CONSTANT_MACROS
+#define __STDC_CONSTANT_MACROS
+#endif
+#ifndef __STDC_LIMIT_MACROS
+#define __STDC_LIMIT_MACROS
+#endif
+#ifndef __STDC_FORMAT_MACROS
+#define __STDC_FORMAT_MACROS
+#endif
+
 /* The following block of code temporarily renames the daemon() function so the
  * compiler does not see the warning associated with it in stdlib.h on OSX
  */