[ValueTracking] Don't use CondContext in dataflow analysis of phi nodes (#100316)
See the following case:
```
define i16 @pr100298() {
entry:
br label %for.inc
for.inc:
%indvar = phi i32 [ -15, %entry ], [ %mask, %for.inc ]
%add = add nsw i32 %indvar, 9
%mask = and i32 %add, 65535
%cmp1 = icmp ugt i32 %mask, 5
br i1 %cmp1, label %for.inc, label %for.end
for.end:
%conv = trunc i32 %add to i16
%cmp2 = icmp ugt i32 %mask, 3
%shl = shl nuw i16 %conv, 14
%res = select i1 %cmp2, i16 %conv, i16 %shl
ret i16 %res
}
```
When computing knownbits of `%shl` with `%cmp2=false`, we cannot use
this condition in the analysis of `%mask (%for.inc -> %for.inc)`.
Fixes https://github.com/llvm/llvm-project/issues/100298.
59eae919c9