Add raw_pwrite_stream type.

This is a raw_ostream that also supports pwrite.
I will be used in a sec.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234895 91177308-0d34-0410-b5e6-96231b3b80d8

unittests/Support/raw_pwrite_stream_test.cpp

@@ -0,0 +1,25 @@
+//===- raw_pwrite_stream_test.cpp - raw_pwrite_stream tests ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "gtest/gtest.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(raw_pwrite_ostreamTest, TestSVector) {
+  SmallString<64> Buffer;
+  raw_svector_ostream OS(Buffer);
+  StringRef Test = "test";
+  OS.pwrite(Test.data(), Test.size(), 0);
+  EXPECT_EQ(Test, OS.str());
+}
+}