LGTM.com - false positive: cpp/unused-local-variable constexpr template parameter

**Description of the false positive**

```
constexpr size_t ZeroMask2 = (ZeroMask & 1 ? 0b11 : 0b00) | (ZeroMask & 2 ? 0b1100 : 0b0000);
ttlet r = f32x4_x64v2_insert(tmp, rhs_);
```
ZeroMask2 is seen as a cpp/unused-local-variable. However it is used as a template parameter to the f32x4_x64v2_insert function.

**URL to the alert on the project page on LGTM.com**

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Here is the github page: https://github.com/ttauri-project/ttauri/blob/0bf4717084fbc7d86d569b9722547884c0ac88e9/src/ttauri/rapid/f32x4_x64v2.hpp#L490-L490