libvixl: Correct build failures on NetBSD

libvixl: Correct build failures on NetBSD

Ensure that C99 macros are defined regardless of the inclusion order of
headers in vixl. This is required at least on NetBSD.

The vixl/globals.h headers defines __STDC_CONSTANT_MACROS and must be
included before other system headers.

This file defines unconditionally the following macros, without altering
the original sources:
 - __STDC_CONSTANT_MACROS
 - __STDC_LIMIT_MACROS
 - __STDC_FORMAT_MACROS

Signed-off-by: Kamil Rytarowski <n54@gmx.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20170514051820.15985-1-n54@gmx.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>