[ELF] Fix incorrect exit status bug exposed by D38283

[bd1976llvm]

Summary

Despite emitting an error the return code is 0 if we can not write to the output file.

https://reviews.llvm.org/D38283 meant that we are now hitting this case.

[ruiu]

LGTM

ELF/Writer.cpp

247–250

error indeed increments ErrorCount, but the code seems to be unnecessarily indirect. I think I prefer

if (auto EC = Buffer->commit()) {
  error(...);
  return;
}

ELF/Writer.cpp

template <class ELFT> void Writer<ELFT>::run() {
   if (ErrorCount)
     return;
 
   // Handle -Map option.
   writeMapFile<ELFT>();
   if (ErrorCount)
     return;
 
   if (auto EC = Buffer->commit())
     error("failed to write to the output file: " + EC.message());
+  if (ErrorCount)
+    return;
 
   // Flush the output streams and exit immediately. A full shutdown
   // is a good test that we are keeping track of all allocated memory,
   // but actually freeing it is a waste of time in a regular linker run.
   if (Config->ExitEarly)
     exitLld(0);
 }