Replace OwningPtr<T> with std::unique_ptr<T>.

This compiles with no changes to clang/lld/lldb with MSVC and includes
overloads to various functions which are used by those projects and llvm
which have OwningPtr's as parameters. This should allow out of tree
projects some time to move. There are also no changes to libs/Target,
which should help out of tree targets have time to move, if necessary.

llvm-svn: 203083
diff --git a/llvm/unittests/IR/ConstantsTest.cpp b/llvm/unittests/IR/ConstantsTest.cpp
index fee38b8..b3aa810 100644
--- a/llvm/unittests/IR/ConstantsTest.cpp
+++ b/llvm/unittests/IR/ConstantsTest.cpp
@@ -162,7 +162,7 @@
   }
 
 TEST(ConstantsTest, AsInstructionsTest) {
-  OwningPtr<Module> M(new Module("MyModule", getGlobalContext()));
+  std::unique_ptr<Module> M(new Module("MyModule", getGlobalContext()));
 
   Type *Int64Ty = Type::getInt64Ty(getGlobalContext());
   Type *Int32Ty = Type::getInt32Ty(getGlobalContext());