[LLVM-C] Add binding to BitcodeReader::getBitcodeProducerString

[vadorovsky]

Add LLVMGetBircodeProducerString function in LLVM C API that binds to BitcodeReader::getBitcodeProducerString in LLVM C++ API.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[tamird]

is it not an error for Producer to be NULL here (and for Err to be non-NULL)?

[vadorovsky]

You're right. I extended the predicate in the if statement above to Ret || Err and handled the lack of Producer as an error.

[tamird]

I'm not sure this is what I meant. I was thinking we'd want the test to be as strict as possible - to me that means no || anywhere.

[vadorovsky]

Alright, how does it look for you now?

[tamird]

This can just be outside the if (Res), right? you always want to print these if they are non-null. Then you can immediately dispose them, and then you can:

int Ret = 0;
if (Res) {
  fprintf(stderr, "LLVMGetBitcodeProducerString(...) returned %d", Res);
  Ret = 1;
}
if (!Producer) {
  fprintf(...)
  Ret = 1;
}
if (Err) {
  ...
}
return Ret;

by the way, do we need a negative test, for the error case? It is not currently exercised.