When building with -Werror,-Wsigned-enum-bitfield clang reports that "enums in the Microsoft ABI are signed integers by default; consider giving the enum type an unsigned underlying type to make this code portable" for these two types.
Under this ABI one bit of an enum bitfield is used by the sign bit. Enum values large enough to overlap that bit would be seen as negative integers if read out into an integer.
There may not be any such reading out at present, but making the underlying type unsigned ensures consistent results across platforms.
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