[CIR] Tolerate identical source and destination in cir.copy (#193852)
The SIBsim4 test in the llvm-test-suite MultiSource tests has code that
initializes a structure with itself. This was triggering a CIR
verifcation error because we were checking for source and destination
addresses matching. Since Clang allows this, this change is updating the
cir.copy operation to allow it.