add missing #includes


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@49020 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Archive/ArchiveWriter.cpp b/lib/Archive/ArchiveWriter.cpp
index 04cc981..c73e170 100644
--- a/lib/Archive/ArchiveWriter.cpp
+++ b/lib/Archive/ArchiveWriter.cpp
@@ -13,6 +13,7 @@
 
 #include "ArchiveInternals.h"
 #include "llvm/Bitcode/ReaderWriter.h"
+#include "llvm/System/MappedFile.h"
 #include "llvm/System/Signals.h"
 #include "llvm/System/Process.h"
 #include "llvm/ModuleProvider.h"