fix PR3859: crash with 'cc -V'

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67472 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Arg.cpp b/lib/Driver/Arg.cpp
index c43c9fb..df75a5d 100644
--- a/lib/Driver/Arg.cpp
+++ b/lib/Driver/Arg.cpp
@@ -162,8 +162,9 @@
     Output.push_back(Args.MakeArgString(Joined.c_str()));
   } else {
     Output.push_back(Args.getArgString(getIndex()));
-    for (unsigned i = 0; i < NumValues; ++i)
-      Output.push_back(Args.getArgString(getIndex() + 1 + i));
+    unsigned limit = std::min(Args.size(), getIndex() + 1 + NumValues);
+    for (unsigned i = getIndex() + 1; i < limit; ++i)
+      Output.push_back(Args.getArgString(i));
   }
 }