[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 ult i8 %neg_x, %x
  =>
%r = icmp slt i8 %x, 0

https://rise4fun.com/Alive/zSuf

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