Update MCLinker to work with LLVM 3.4.

This corresponds to merging upstream MCLinker with the following SHA:
6dcbf36cdb146d6f175ba2f18a9004753cafeaff

Change-Id: I1bc8c2ce4accc563450bc71ee295a6e47a0c0469

include/mcld/Support/FileOutputBuffer.h

diff --git a/include/mcld/Support/FileOutputBuffer.h b/include/mcld/Support/FileOutputBuffer.h
new file mode 100644
index 0000000..a49ffb7
--- /dev/null
+++ b/include/mcld/Support/FileOutputBuffer.h
@@ -0,0 +1,72 @@
+//===- FileOutputBuffer.h -------------------------------------------------===//
+//
+//                     the mclinker project
+//
+// this file is distributed under the university of illinois open source
+// license. see license.txt for details.
+//
+//===----------------------------------------------------------------------===//
+#ifndef MCLD_SUPPORT_FILEOUTPUTBUFFER_H
+#define MCLD_SUPPORT_FILEOUTPUTBUFFER_H
+#ifdef ENABLE_UNITTEST
+#include <gtest.h>
+#endif
+
+#include <mcld/Support/MemoryRegion.h>
+#include <llvm/ADT/OwningPtr.h>
+#include <llvm/ADT/StringRef.h>
+#include <llvm/Support/DataTypes.h>
+#include <llvm/Support/FileSystem.h>
+#include <llvm/Support/system_error.h>
+
+namespace mcld {
+
+class FileHandle;
+
+/// FileOutputBuffer - This interface is borrowed from llvm bassically, and we
+/// may use ostream to emit output later.
+class FileOutputBuffer {
+public:
+  /// Factory method to create an OutputBuffer object which manages a read/write
+  /// buffer of the specified size. When committed, the buffer will be written
+  /// to the file at the specified path.
+  static llvm::error_code create(FileHandle& pFileHandle,
+                                 size_t pSize,
+                                 llvm::OwningPtr<FileOutputBuffer>& pResult);
+
+  /// Returns a pointer to the start of the buffer.
+  uint8_t* getBufferStart() {
+    return (uint8_t*)m_pRegion->data();
+  }
+
+  /// Returns a pointer to the end of the buffer.
+  uint8_t* getBufferEnd() {
+    return (uint8_t*)m_pRegion->data() + m_pRegion->size();
+  }
+
+  /// Returns size of the buffer.
+  size_t getBufferSize() const {
+    return m_pRegion->size();
+  }
+
+  MemoryRegion request(size_t pOffset, size_t pLength);
+
+  /// Returns path where file will show up if buffer is committed.
+  llvm::StringRef getPath() const;
+
+  ~FileOutputBuffer();
+
+private:
+  FileOutputBuffer(const FileOutputBuffer &);
+  FileOutputBuffer &operator=(const FileOutputBuffer &);
+
+  FileOutputBuffer(llvm::sys::fs::mapped_file_region* pRegion,
+                   FileHandle& pFileHandle);
+
+  llvm::OwningPtr<llvm::sys::fs::mapped_file_region> m_pRegion;
+  FileHandle& m_FileHandle;
+};
+
+} // namespace mcld
+
+#endif