wchar_t is unsigned on ARM platforms, and signed pretty much everywhere
else. On signed platforms, nm ends up with bogus upper bits set if we
did in-fact have a valid CS2 or CS3 (MSB set). Mask just the low byte
to avoid sign bit garbage.
Bare basic test of converting a CS2 widechar in eucCN, which would
previously kick back an EILSEQ.
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