_d_arraysetlengthT should return the new length not the array

[Vild]

Needed for: dlang/dmd#10106

_d_arraysetlengthT needs to return the new length of array instead of the array itself.
Without this change the dmd patch will fail on this testcase: https://github.com/dlang/dmd/blob/master/test/compilable/compile1.d#L860

[dlang-bot]

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