[ValueTracking] improve analysis for fdiv with same operands

(The 'nnan' variant of this pattern is already tested to produce '1.0'.)

https://alive2.llvm.org/ce/z/D4hPBy

define i1 @src(float %x, i32 %y) {
%0:
  %d = fdiv float %x, %x
  %uge = fcmp uge float %d, 0.000000
  ret i1 %uge
}
=>
define i1 @tgt(float %x, i32 %y) {
%0:
  ret i1 1
}
Transformation seems to be correct!