We are already including -D__STDC_LIMIT_MACROS in the global CXXFLAGS,
so it makes sense to do the same for -D__STDC_CONSTANT_MACROS and
-D__STDC_FORMAT_MACROS instead of limiting that to libvixl.
The -Wno-sign-compare option can also be removed since GCC 4.6 is not
supported anymore.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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