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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216002 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/MemoryBuffer.h

@@ -24,9 +24,11 @@
 #include <system_error>
 
 namespace llvm {
-/// This interface provides simple read-only access to a block/ of memory, and
+class MemoryBufferRef;
+
+/// This interface provides simple read-only access to a block of memory, and
 /// provides simple methods for reading files and standard input into a memory
-/// buffer. In addition to basic access to the characters in the file, this
+/// buffer.  In addition to basic access to the characters in the file, this
 /// interface guarantees you can read one character past the end of the file,
 /// and that this character will read as '\0'.
 ///
@@ -136,7 +138,27 @@ public:
 
   /// Return information on the memory mechanism used to support the
   /// MemoryBuffer.
-  virtual BufferKind getBufferKind() const = 0;  
+  virtual BufferKind getBufferKind() const = 0;
+
+  MemoryBufferRef getMemBufferRef() const;
+};
+
+class MemoryBufferRef {
+  StringRef Buffer;
+  StringRef Identifier;
+
+public:
+  MemoryBufferRef() {}
+  MemoryBufferRef(StringRef Buffer, StringRef Identifier)
+      : Buffer(Buffer), Identifier(Identifier) {}
+
+  StringRef getBuffer() const { return Buffer; }
+
+  StringRef getBufferIdentifier() const { return Identifier; }
+
+  const char *getBufferStart() const { return Buffer.begin(); }
+  const char *getBufferEnd() const { return Buffer.end(); }
+  size_t getBufferSize() const { return Buffer.size(); }
 };
 
 // Create wrappers for C Binding types (see CBindingWrapping.h).