Don't own the buffer in object::Binary.

Owning the buffer is somewhat inflexible. Some Binaries have sub Binaries
(like Archive) and we had to create dummy buffers just to handle that. It is
also a bad fit for IRObjectFile where the Module wants to own the buffer too.

Keeping this ownership would make supporting IR inside native objects
particularly painful.

This patch focuses in lib/Object. If something elsewhere used to own an Binary,
now it also owns a MemoryBuffer.

This patch introduces a few new types.

* MemoryBufferRef. This is just a pair of StringRefs for the data and name.
  This is to MemoryBuffer as StringRef is to std::string.
* OwningBinary. A combination of Binary and a MemoryBuffer. This is needed
  for convenience functions that take a filename and return both the
  buffer and the Binary using that buffer.

The C api now uses OwningBinary to avoid any change in semantics. I will start
a new thread to see if we want to change it and how.

llvm-svn: 216002
diff --git a/llvm/unittests/ExecutionEngine/MCJIT/MCJITObjectCacheTest.cpp b/llvm/unittests/ExecutionEngine/MCJIT/MCJITObjectCacheTest.cpp
index 5eebddb..f230fb8 100644
--- a/llvm/unittests/ExecutionEngine/MCJIT/MCJITObjectCacheTest.cpp
+++ b/llvm/unittests/ExecutionEngine/MCJIT/MCJITObjectCacheTest.cpp
@@ -25,7 +25,7 @@
 public:
   TestObjectCache() : DuplicateInserted(false) { }
 
-  virtual void notifyObjectCompiled(const Module *M, const MemoryBuffer *Obj) {
+  void notifyObjectCompiled(const Module *M, MemoryBufferRef Obj) override {
     // If we've seen this module before, note that.
     const std::string ModuleID = M->getModuleIdentifier();
     if (ObjMap.find(ModuleID) != ObjMap.end())
@@ -63,10 +63,10 @@
   }
 
 private:
-  MemoryBuffer *copyBuffer(const MemoryBuffer *Buf) {
+  MemoryBuffer *copyBuffer(MemoryBufferRef Buf) {
     // Create a local copy of the buffer.
     std::unique_ptr<MemoryBuffer> NewBuffer(
-        MemoryBuffer::getMemBufferCopy(Buf->getBuffer()));
+        MemoryBuffer::getMemBufferCopy(Buf.getBuffer()));
     MemoryBuffer *Ret = NewBuffer.get();
     AllocatedBuffers.push_back(std::move(NewBuffer));
     return Ret;