Since the version v1.5.0 of sse2neon the functionality for denormals
flushing is implemented in the library. This commit makes it so the
_MM_SET_FLUSH_ZERO_MODE and _MM_SET_DENORMALS_ZERO_MODE are used from
the ss2neon if available.
This solves macro re-definition when a newer sse2neon is used.
The change is implemented in a way that both current and new sse2neon
are supported.