Add missing include found by the bots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184354 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-ar/Archive.h

@@ -23,6 +23,7 @@
 #include "llvm/Support/TimeValue.h"
 #include <map>
 #include <set>
+#include <vector.h>
 
 namespace llvm {
   class MemoryBuffer;