The guest's wchar_t is 16 bits, but wcslen, wcscmp, wcsncmp, wcscpy, wcsncpy, wcschr, wcsrchr, wcsstr, wcspbrk, wcsspn and the wmem functions forwarded to the host's wchar_t functions, which use 32-bit units on Linux. Implement them on char16_t. The wide conversions that still use the host's wchar_t are listed in TechnicalDebt.
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