Fix various minor issues with upstream libvixl so that it will compile
successfully on the platforms QEMU cares about:
 * remove unused GBytes constant (it clashes with the glib headers)
 * fix suffixes on constants to use 'LL' for 64 bit constants so
   we can compile on 32 bit hosts
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <rth@twiddle.net>