Reapply [InstCombine] Remove one-use limitation from X-Y==0 fold

This is a recommit without changes. I originally reverted this
due to a significant code-size regression on tramp3d-v4, however
further investigation showed that in the tramp3d-v4 case this
change enables additional optimizations (in particular more
jump threading), which happens to reduce the size of a function
just enough to be eligible for inlining at hot callsites, which
results in the code size increase. As such, this was just bad
luck.

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This one-use limitation is artificial, we do not increase
instruction count if we perform the fold with multiple uses. The
motivating case is shown in @sub_eq_zero_select, where the one-use
limitation causes us to miss a subsequent select fold.

I believe the backend is pretty good about reusing flag-producing
subs for cmps with same operands, so I think doing this is fine.

Differential Revision: https://reviews.llvm.org/D120337

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