Fix unicode_aswidechar() for 4b unicode and 2b wchar_t (AIX).

--HG--
branch : 3.2
extra : amend_source : 9a9747ab38c1ed3d5d9baeb8c3b276622c8e0944
ref #19855: skip uuid test_find_mac on non-Posix as in later branches

--HG--
branch : 3.2
extra : amend_source : a3fa70823c46f9d5ae2e117cc472eb2c61a8f178