Older versions of clang have missing runtime functions for arithmetic
with -fsanitize=undefined (see 464e3671f9d5c), so we cannot use
__int128_t for implementing Int128. But __int128_t is present,
data movement works, and it can be used for atomic128.
Probe for both CONFIG_INT128_TYPE and CONFIG_INT128, adjust
qemu/int128.h to define Int128Alias if CONFIG_INT128_TYPE,
and adjust the meson probe for atomics to use has_int128_type.
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
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