Add AlignedAllocation.h.

I forgot to "git add" it in r308496.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@308498 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/AlignedAllocation.h

@@ -0,0 +1,44 @@
+//===--- AlignedAllocation.h - Aligned Allocation ---------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief Defines a function that returns the minimum OS versions supporting
+/// C++17's aligned allocation functions.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_BASIC_ALIGNED_ALLOCATION_H
+#define LLVM_CLANG_BASIC_ALIGNED_ALLOCATION_H
+
+#include "clang/Basic/VersionTuple.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/Support/ErrorHandling.h"
+
+namespace clang {
+
+inline VersionTuple alignedAllocMinVersion(llvm::Triple::OSType OS) {
+  switch (OS) {
+  default:
+    break;
+  case llvm::Triple::Darwin:
+  case llvm::Triple::MacOSX: // Earliest supporting version is 10.13.
+    return VersionTuple(10U, 13U);
+  case llvm::Triple::IOS:
+  case llvm::Triple::TvOS: // Earliest supporting version is 11.0.0.
+    return VersionTuple(11U);
+  case llvm::Triple::WatchOS: // Earliest supporting version is 4.0.0.
+    return VersionTuple(4U);
+  }
+
+  llvm_unreachable("Unexpected OS");
+}
+
+} // end namespace clang
+
+#endif // LLVM_CLANG_BASIC_ALIGNED_ALLOCATION_H