Make llvm-ar behave like ar, if you create an empty archive, ar creates an empty archive. llvm-ar would not generate an output file in this case

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47733 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-ar/llvm-ar.cpp

@@ -717,6 +717,7 @@ int main(int argc, char **argv) {
       if (!Create)
         std::cerr << argv[0] << ": creating " << ArchivePath.toString() << "\n";
       TheArchive = Archive::CreateEmpty(ArchivePath);
+      TheArchive->writeToDisk();
     } else {
       std::string Error;
       TheArchive = Archive::OpenAndLoad(ArchivePath, &Error);