Pass a MemoryBufferRef when we can avoid taking ownership.

The attached patch simplifies a few interfaces that don't need to take
ownership of a buffer.

For example, both parseAssembly and parseBitcodeFile will parse the
entire buffer before returning. There is no need to take ownership.

Using a MemoryBufferRef makes it obvious in the type signature that
there is no ownership transfer.

llvm-svn: 216488

llvm/lib/IR/Module.cpp

@@ -413,13 +413,10 @@ std::error_code Module::materializeAll() {
   return Materializer->MaterializeModule(this);
 }
 
-std::error_code Module::materializeAllPermanently(bool ReleaseBuffer) {
+std::error_code Module::materializeAllPermanently() {
   if (std::error_code EC = materializeAll())
     return EC;
 
-  if (ReleaseBuffer)
-    Materializer->releaseBuffer();
-
   Materializer.reset();
   return std::error_code();
 }