[clang-offload-bundler] fix "no output file" issue with -outputs

Fix backward compatibility issue due to D120662.

Change-Id: I7cd0f704aabbaac7dcf59fd4b73b4f0e0cdfa69f

Reviewed By: yaxunl, saiislam

Differential Revision: https://reviews.llvm.org/D123387

clang/tools/clang-offload-bundler/ClangOffloadBundler.cpp

@@ -1450,7 +1450,7 @@ int main(int argc, const char **argv) {
     return 0;
   }
 
-  if (OutputFileNames.getNumOccurrences() == 0) {
+  if (OutputFileNames.size() == 0) {
     reportError(
         createStringError(errc::invalid_argument, "no output file specified!"));
   }