[GlobalOpt][Evaluator] Don't create bitcast for same type (PR52994)

isBitOrNoopPointerCastable() returns true if the types are the
same, but it's not actually possible to create a bitcast for all
such types. The assumption seems to be that the user will omit
creating the cast in that case, as it is unnecessary.

Fixes https://github.com/llvm/llvm-project/issues/52994.