[MCJIT] Fix case of Error::success being passed to report_fatal_error.

[jascha]

Summary

MCJIT::getSymbolAddress was handling a non-fatal error condition of JITSymbol
as fatal. JITSymbol::operator bool returns false if no address is available
but no error is set. This can occur e.g. if the symbol name was not found.

[lhames]

Looks good to me. Thanks Jascha!

Do you have commit access? If not, do you mind if I commit on your behalf?

[jascha]

I don't have commit access, please do commit.
Thank you.

[lhames]

This was committed in r339809.

lib/ExecutionEngine/MCJIT/MCJIT.cpp

 
 uint64_t MCJIT::getSymbolAddress(const std::string &Name,
                                  bool CheckFunctionsOnly) {
   std::string MangledName;
   {
     raw_string_ostream MangledNameStream(MangledName);
     Mangler::getNameWithPrefix(MangledNameStream, Name, getDataLayout());
   }
-  if (auto Sym = findSymbol(MangledName, CheckFunctionsOnly)) {
+  auto Sym = findSymbol(MangledName, CheckFunctionsOnly);
+  if (Sym) {
     if (auto AddrOrErr = Sym.getAddress())
       return *AddrOrErr;
     else
       report_fatal_error(AddrOrErr.takeError());
-  } else
-    report_fatal_error(Sym.takeError());
+  } else if (auto err = Sym.takeError())
+    report_fatal_error(std::move(err));
+  return 0;
 }
 
 JITSymbol MCJIT::findSymbol(const std::string &Name,
                             bool CheckFunctionsOnly) {
   MutexGuard locked(lock);
 
   // First, check to see if we already have this symbol.
   if (auto Sym = findExistingSymbol(Name))