[ValueTracking] Fix an assert from r340480.

We need to allow ConstantExpr Selects in addition to SelectInst.

I'll try to put together a test case, but I wanted to fix the issues being reported.

Fixes PR38677

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340546 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed