[llvm] Replace m_SpecificInt(1) with m_One() (NFC) (PR #102173)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> > m_One allows undefined elements. m_SpecificInt does not. Is the actually NFC?
> 
> m_One() is actually implemented using SpecificInt_match, which means it has identical behavior to m_SpecificInt(1).

Isn't that just the SDPatternMatch variant?

PatternMatch m_One() uses cst_pred_ty which AllowsPoison by default while m_SpecificInt uses specific_intval64 which doesn't

https://github.com/llvm/llvm-project/pull/102173