Add LLVM Legalization for tir.erf

[EnigmaWH]

Description

This PR adds LLVM legalization support for tir.erf using the Abramowitz and Stegun approximation, which avoids the precision issues found in the tanh approximation based implementation.
@Hzfengsy @tqchen @Lunderberg @mshr-h

[cbalint13]

Hi @Gokulnathsrinivasanmcw ,

Thanks for the addition, erf is welcome !

There is another concurent proposal open here (have tests, didnt pass lint).
Just please add a test case for erf and make sure all required CI tasks are in green.

[EnigmaWH]

Hi @Gokulnathsrinivasanmcw ,

Thanks for the addition, erf is welcome !

There is another concurent proposal open here (have tests, didnt pass lint). Jut please add a test case for erf and make sure all required CI tasks are in green.

Sure, @cbalint13 — I’ll check that out. Thanks for letting me know!

[EnigmaWH]

Hi @Gokulnathsrinivasanmcw ,

Thanks for the addition, erf is welcome !

There is another concurent proposal open here (have tests, didnt pass lint). Jut please add a test case for erf and make sure all required CI tasks are in green.

Hi @cbalint13, I've added a test case.

[cbalint13]

Thank you @Gokulnathsrinivasanmcw !