[InstCombine] (-NSW x) u> x --> x s> 0 (PR39480)

Name: (-x) u> x  -->  x s> 0
%neg_x = sub nsw i8 0, %x ; %x must not be INT_MIN
%r = icmp ugt i8 %neg_x, %x
  =>
%r = icmp sgt i8 %x, 0

https://rise4fun.com/Alive/Raea

https://bugs.llvm.org/show_bug.cgi?id=39480