[Reflection] Start fleshing out the remote mirrors library

- Don't depend on LLVM Support and swiftBasic as this will bring in
  llvmSupport and other heavy dependencies, which we don't build for
  non-host architectures right now anyway.

- Add a reader template that works with the same (albeit somewhat
  clunky) interface in-process with the runtime and remotely, by having
  the memory tool supply a function that will copy data from the remote
  process.

- Add a Buffer type to abstract indirecting pointers in a remote address
  space, which is handled by the memory reader.

- Start sketching out the C remote mirrors interface.

include/swift/SwiftReflection/SwiftReflection.h

@@ -0,0 +1,72 @@
+//===--- SwiftReflection.h - Public remote reflection interface -*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This header declares functions in the libswiftReflection library,
+/// which provides mechanisms for reflecting heap information in a
+/// remote Swift process.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_REFLECTION_SWIFT_REFLECTION_H
+#define SWIFT_REFLECTION_SWIFT_REFLECTION_H
+
+/// Major version changes when there are ABI or source incompatible changes.
+#define SWIFT_REFLECTION_VERSION_MAJOR 3
+
+/// Minor version changes when new APIs are added in ABI- and source-compatible
+/// way.
+#define SWIFT_REFLECTION_VERSION_MINOR 0
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/// \brief Represents the __swift{n}_reflect section of an image.
+///
+/// If this section is virtually mapped, the following corresponding sections
+/// should also be mapped into the current address space:
+///
+/// __swift{n}_typeref
+/// --swift{n}_reflstr
+///
+/// where {n} is SWIFT_REFLECTION_VERSION_MAJOR.
+typedef struct ReflectionSection {
+  const char *ImageName;
+  void *Begin;
+  void *End;
+} ReflectionSection;
+
+/// \brief An opaque pointer to a context which maintains state and
+/// caching of reflection structure for heap instances.
+typedef struct ReflectionContext *ReflectionContextRef;
+
+/// \brief Copies Size bytes from the Source in the target
+/// address space to Dest.
+typedef size_t (*CopyFunction)(uintptr_t Source, void *Dest, size_t Size);
+
+/// \returns An opaque reflection context.
+ReflectionContextRef swift_reflection_createReflectionContext(
+    ReflectionSection *Sections, size_t NumSections, CopyFunction Copier);
+
+/// Clear any caching of field type information for all known heap instances.
+void swift_reflection_clearCaches(ReflectionContexRef Context);
+
+/// Destroys an opaque reflection context.
+void swift_reflection_destroyReflectionContext(ReflectionContexRef Context);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+#endif // SWIFT_REFLECTION_SWIFT_REFLECTION_H
+