[LV] Ignore user-specified interleave count when unsafe. (#153009)

When an VF is specified via a loop hint, it will be clamped to a safe
VF or ignored if it is found to be unsafe. This is not the case for
user-specified interleave counts, which can lead to loops such as
the following with a memory dependence being vectorised with
interleaving:

```
#pragma clang loop interleave_count(4)
for (int i = 4; i < LEN; i++)
    b[i] = b[i - 4] + a[i];
```

According to [1], loop hints are ignored if they are not safe to apply.

This patch adds a check to prevent vectorisation with interleaving if
isSafeForAnyVectorWidth() returns false. This is already checked in
selectInterleaveCount().

[1]
https://llvm.org/docs/LangRef.html#llvm-loop-vectorize-and-llvm-loop-interleave

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