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Auto merge of #99747 - ankane:float_gamma, r=workingjubilee
Add gamma function to f32 and f64
Adds the [gamma function](https://en.wikipedia.org/wiki/Gamma_function) to `f32` and `f64` (`tgamma` and `tgammaf` from C).
Refs:
- https://github.com/rust-lang/rfcs/issues/864
- https://github.com/rust-lang/rust/issues/18271
